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BIOLOGY ESSAYS FOR EASY REVISION. 1(a

Describe the digestion of a starchy meal along the human alimentary canal. S (13 mks) Answer-Starch in food is first broken down in the mouth by action of teeth/ chewing; This increases the surface area exposed enzyme action; saliva contains salivary amylase which breaks down some starch to maltose; saliva has a slightly alkaline pH which is optimum for the enzyme; The food moves down to the oespophagus and stomach; where the acidic pH, due presence of dilute Hcl, prevents further action of salivary amylase; In the duodenum, pancreatic amylase continues digestion of starch to maltose; Pancreatic amylase is produced in the pancrease; and enters the duodenum through pancreatic ducts; the acidic chyme is neutralized by the sodium bicarbonate in bile/ pancreatic juice; Maltose digestion continues in the ileum; whose walls secrete succus entericus/ intestinal juice; which contains enzyme maltase; which breaks down maltose to glucose; (Max 13 marks) (b) Describe the process of urea formation. (7marks) answer Excess amino acids / proteins; are transported to the liver 2. (a) Describe how gaseous exchange occurs in terrestrial plants. (13 marks) Answer Gaseous exchange takes place in a spongy mesophyl During the day air diffuses into large air spaces of spongy mesophyll; through stomata; the Carbon (IV) Oxide in the air diffuses into Photosynthetic cells; in solution form; during photosynthesis Carbon (iv) Oxide is used while oxygen is produced. Oxygen diffuses out of the leaf; through stomata; During the night; air diffuses into the air spaces (of spongy mesophyll), the air dissolves into film of moisture; then oxygen diffuses into the cells; and is used in respiration during which carbon (iv) oxide is produced, the Carbon (iv) Oxide diffuses out of the leaf; through stomata; due to concentration/diffusion gradient; Gaseous exchange takes place through epidermis (of young leaves and stems); epidermis of the root carries out gaseous exchange with air in the soil; some plants have pneumatophores/breathing roots; in which gaseous exchange occurs through lenticels; (found in

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Essay writing in biology: An example of effective student learning?

• Published: December 1996
• Volume 26 , pages 437–459, ( 1996 )

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• Petrus Zeegers 1 &
• Lynne Giles 1  

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The views of first-year biology students ( N =337) on an essay writing assignment were evaluated by means of a questionnaire. The students were asked to reflect on the strategies they employed, the number and type of resources used, their areas of difficulty and to evaluate their own performance. The data were used to elucidate possible areas of discrepancy between the approach taken by the students and that suggested by the Biology Department via information in student manuals and evaluation criteria. The data were also compared to similar studies on student writing previously reported for students of psychology and history. Finally a series of recommendations is made to help staff to allow their students to develop improved writing strategies, minimise the possible difficulties encountered and allow the writing exercise to fulfil its desired outcome, that of being an integral part of the process of learning.

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Zeegers, P., Giles, L. Essay writing in biology: An example of effective student learning?. Research in Science Education 26 , 437–459 (1996). https://doi.org/10.1007/BF02357454

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Review Essays for the Biological sciences

A review essay for the biological sciences serves to discuss and synthesize key findings on a particular subject. Review papers are helpful to the writer and their colleagues in gaining critical awareness in specialized fields that may or may not be their own.

This guide explains what a review essay is and identifies several approaches to writing a review essay. Although much of the information is geared directly to the biological sciences, it is generally applicable to review essays in all fields.

What is a Review Essay?

A review essay is a synthesis of primary sources (mainly research papers presented in academic journals) on a given topic. A biological review essay demonstrates that the writer has thorough understanding of the literature and can formulate a useful analysis. While no new research is presented by the writer, the field benefits from the review by recieving a new perspective. There are several approaches one may take when writing a biological review:

A State of the art review

A state of the art review considers mainly the most current research in a given area. The review may offer new perspectives on an issue or point out an area in need of further research.

A Historical review

A historical review is a survey of the development of a particular field of study. It may examine the early stages of the field, key findings to present, key theoretical models and their evolution, etc.

A Comparison of perspectives review

A comparison of perspectives review contrasts various ways of looking at a certain topic. If in fact there is a debate over some process or idea, a comparison of perspectives review may illustrate the research that supports both sides. A comparison of perspectives review may introduce a new perspective by way of comparing it to another.

A Synthesis of two fields review

Many times researchers in different fields may be working on similar problems. A synthesis of two fields review provides insights into a given topic based on a review of the literature from two or more disciplines.

A Theoretical model building review

A theoretical model building review examines the literature within a given area with the intention of developing new theoretical assumptions.

Key Considerations for Writing a Biological Review Essay

This guide will inform you of certain things not to miss when writing a review essay. It will also give you some information about using and documenting your sources.

Keep your focus narrow.

When writing a review essay it is important to keep the scope of the topic narrow enough so that you can discuss it thoroughly. For example a topic such as air quality in factories could be narrowed significantly to something like carbon dioxide levels in auto manufacturing plants .

A good way to narrow your focus is to start with a broad topic that is of some interest to you, then read some of the literature in the field. Look for a thread of the discussion that points to a more specific topic.

Analyze, synthesize, and interpret.

A review essay is not a pure summary of the information you read for your review. You are required to analyze, synthesize, and interpret the information you read in some meaningful way.

It is not enough to simply present the material you have found, you must go beyond that and explain its relevance and significance to the topic at hand.

Establish a clear thesis from the onset of your writing and examine which pieces of your reading help you in developing and supporting the ideas in your thesis.

Use only academic sources.

A review essay reviews the academic body of literature—articles and research presented in academic journals. Lay periodicals such as, Discover , Scientific America , or Popular Science , are not adequate sources for an academic review essay.

If you are having trouble finding the academic journals in your field, ask one of your professors or a reference librarian.

Document your sources.

The material that you discuss in a review essay is obviously not your own, therefore it is crucial to document your sources properly. Proper documentation is crucial for two reasons: 1. It prevents the writer from being accused of plagiarism and 2. It gives the reader the opportunity to locate the sources the writer has reviewed because they may find them valuable in their own academic pursuits. Proper documentation depends on which style guide you are following.

Quote sparingly and properly.

No one wants to read a paper that is simply a string of quotes; reserve direct quotations for when you want to create a big impact. Often times the way a quote is written will not fit with the language or the style of your paper so paraphrase the authors words carefully and verbage as necessary to create a well formed paragraph.

Choose an informative title.

The title you choose for your review essay should give some indication of what lies ahead for the reader. You might consider the process you took in narrowing your topic to help you with your title—think of the title as something specific rather than a vague representation of your paper's topic. For example the title Wastewater Treatment might be more informative if rewritten as The Removal of Cloroform Bacteria as Practiced by California's Municipal Water Treatment Facilities .

Consider your audience.

More than likely your audience will be your academic peers, therefore you can make a couple assumptions and choose a writing style that suits the audience. Though your audience may lack the detailed knowledge you have about your topic, they do have similar background knowledge to you. You can assume that you audience understands much of the technical language you have to use to write about your topic and you do not have to go into great detail about background information.

Elements of a Review Essay

This guide explains each section of a review essay and gives specific information about what should be included in each.

On the title page include the title, your name, and the date. Your instructor may have additional requirements (such as the course number, etc.) so be sure to follow the guidelines on the assignment sheet. Professional journals may also have more specific requirements for the title page.

An abstract is a brief summary of your review. The abstract should include only the main points of your review. Think of the abstract as a chance for the reader to preview your paper and decide if they want to read on for the details.

Introduction

The introduction of your review should accomplish three things:

• It may sound redundant to "introduce" your topic in the introduction, but often times writer's fail to do so. Let the reader in on background information specific to the topic, define terms that may be unfamiliar to them, explain the scope of the discussion, and your purpose for writing the review.
• Think of your review essay as a statement in the larger conversation of your academic community. Your review is your way of entering into that conversation and it is important to briefly address why your review is relevant to the discussion. You may feel the relevance is obvious because you are so familiar with the topic, but your readers have not yet established that familiarity.
• The thesis is the main idea that you want to get across to your reader. your thesis should be a clear statement of what you intend to prove or illustrate by your review. By revealing your thesis in the introduction the reader knows what to expect in the rest of the paper.

The discussion section is the body of your paper. The discussion section contains information that develops and supports your thesis. While there is no particular form that a discussion section must take there are several considerations that a writer must follow when building a discussion.

• A review essay is not simply a summary of literature you have reviewed. Be careful not to leave out your own analysis of the ideas presented in the literature. Synthesize the material from all the works—what are the connections you see, or the connections you are trying to illustrate, among your readings.

A review essay is not a pure summary of the information you read for your review. You are required to analyze, synthesize, and interpret the information you read in some meaningful way. It is not enough to simply present the material you have found, you must go beyond that and explain its relevance and significance to the topic at hand. Establish a clear thesis from the onset of your writing and examine which pieces of your reading help you in developing and supporting the ideas in your thesis.

• Keep your discussion focused on your topic and more importantly your thesis. Don't let tangents or extraneous material get in the way of a concise, coherent discussion. A well focused paper is crucial in getting your message across to your reader.
• Keeping your points organized makes it easier for the reader to follow along and make sense of your review. Start each paragraph with a topic sentence that relates back to your thesis. The headings used for this guide give you some idea of how to organize the overall paper, but as far as the discussion section goes use meaningful subheadings that relate to your content to organize your points.
• Your thesis should illustrate your objectives in writing the review and your discussion should serve to accomplish your objectives. Make sure your keep your discussion related to the thesis in order to meet your objectives. If you find that your discussion does not relate so much to your thesis, don't panic, you might want to revise your thesis instead of reworking the discussion.

Conclusions

Because the conclusions section often gets left for last it is often the weakest part of a student review essay. It is as crucial a part of the paper as any and should be treated as such.

A good conclusion should illustrate the key connections between your major points and your thesis as well as they key connections between your thesis and the broader discussion—what is the significance of your paper in a larger context? Make some conclusions —where have you arrived as a result of writing this paper?

Be careful not to present any new information in the conclusion section.

Here you report all the works you have cited in your paper. The format for a references page varies by discipline as does how you should cite your references within the paper.

Bastek, Neal. (1999). Review Essays for the Biological Sciences. Writing@CSU . Colorado State University. https://writing.colostate.edu/guides/guide.cfm?guideid=79

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This is a collection of free biology worksheets, notes, handouts, slides, study guides and quizzes. Most content targets high school, AP biology, genetics, anatomy/physiology, immunology, and biology 101 and 102 in college. There is also biochemistry and physics for biologists. However, some resources are at the grade school and middle school level.

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Anatomy and Physiology

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Label the Digestive System

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Plasmid Mapping

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• Genetic Codon Chart [ PNG ][ PDF ]
• RNA vs DNA [ JPG ]

Use labelled diagrams as study guides.

Ecosystems Worksheet

Levels of Organization (Ecosystem)

Primary Succession

Secondary Succession

Label the Insect

Label the Bee

Chicken Life Cycle (Basic)

Bird Life Cycle (Basic)

Butterfly Life Cycle

• Biotic and Abiotic Factors [ worksheet PDF ][ worksheet Google Apps ][ worksheet PNG ][ answers PNG ]
• Kingdoms of Life Graphic [ PNG ]
• Autotroph vs Heterotroph Graphic [ PNG ]
• Commensalism Definition and Examples [ PNG ]
• Difference Between Butterflies and Moths [ JPG ]
• Difference Between Bugs and Insects [ PNG ]

Parasitology

Schistosome Life Cycle

Schistosome Anatomy

• Giardia Life Cycle [ worksheet Google Apps ][ worksheet PDF ][ worksheet PNG ][ answers PNG ]

Physical Science for Biology

There is also an entire section devoted to physical science worksheets and study guides.

• Adhesion vs Cohesion Graphic [ PNG ]
• What Is Entropy? [ PNG ]
• Freezing Point of Water [ PNG ]

Biology Labs

• How to Extract DNA From a Banana [ PNG ]

Biology Word Search Puzzles

• DNA Replication Word Search
• Gel Electrophoresis Word Search
• Citrus Fruits
• General Biology Word Search Puzzle [ PNG ]
• Life Science Word Search [ PNG ][ PDF ]
• Cell Biology Word Search [ PNG ][ PDF ]
• Amino Acid Word Search [ PNG ][ PDF ]
• Biome Word Search [ PNG ][ PDF ]
• Environmental Science Word Search [ PNG ][ PDF ]
• Photosynthesis Word Search [ PNG ]
• Human Skeleton Bones Word Search [ PNG ]
• Dinosaur Word Search [ PNG ][ PDF ]
• Different Dinosaur Word Search [ PNG ][ PDF ]
• Wild Cats Word Search [ PNG ][ PDF ]
• Shark Word Search [ PNG ]
• Trees Word Search [ PNG ][ PDF ]
• Flowers Word Search [ PNG ][ PDF ]
• Butterfly Word Search [ PNG ][ PDF ]
• Genetics Word Search [ PNG ][ PDF ]

Miscellaneous Biology Notes and Resouces

• How Long Can Germs Live on Surfaces? [ PNG ]
• 10 Radioactive Foods [ PNG ]
• Examples of Organic Compounds [ PNG ]

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Biology KCSE Essay Questions and Answers Paper 2; Over 1,000

KCSE BIOLOGY PAPPER TWO 231/2 -ESSAYS FROM 1995 -2023

  a). Describe how insect pollinated flowers are adapted to pollination ( KCSE1995)

• Progesterone
• Luteinizinghormone
• Describe how excretion takes place in: ( KCSE1995)
• MammalianKidneys
• Greenplants
• a).Explainhowthemammalianskinisadaptedtoperformitsfunctions (20marks; KCSE 1996)

b). Describe how new plants arise by asexual reproduction (20 marks; KCSE 1996)

• a). What is parasitism? (KCSE1997)

b). Describe how the tapeworm is adapted to a parasitic mode of life (KCSE 1997)

• a). What is meant by the term digestion? (KCSE1997 )

b). Describe how the mammalian small intestine is adapted to its function (KCSE 1997)

• Discuss the various evidences, which show that evolution has taken place (20 marks; KCSE 1998)
• Explain how the mammalian intestines are adapted to perform their function (20 marks; KCSE 1998)
• a). Describethe:
• Process of inhalation in mammals ( KCSE 1999)
• Mechanisms of opening and closing of stomata in plants (KCSE1999)

b). Explain how the various activities of man have caused pollution of air (20 marks; KCSE 1999)

• a). Describe the role of hormones in the human menstrual cycle (20 marks; KCSE2000)

b). How are leaves of mesophytes suited to their functions (20 marks; KCSE 2000)

• a). State the functions of the following parts of the mammalian ear; (KCSE2001)
• Tympanicmembrane
• Eustachiantube
• Earossicles

b). Describe how semicircular canals perform their functions (KCSE 2001 )

• a). Describe the process of fertilization in a flowering plant ( KCSE2001)

b). State the change that take place in a flower after fertilization ( KCSE 2001)

• a). Describe the role of hormones in the growth and development of plants (20 marks; KCSE 2002)
• a). Name three types of skeletons found in multicellular animals ( KCSE2002)

b). Describe how the cervical, lumbar and sacral vertebrae are suited to their functions

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(KCSE 2002)

• a). Describe the functions of the various parts of the human eye (20 marks; KCSE2003)

                                                                                                                                         1 | P a ge

(b). Describe how fruits and seeds are suited to their modes of dispersal (20 marks; KCSE 2003)

• a). How is the mammalian skin adapted to its functions? (20 marks; KCSE2004)

b). Explain how a biotic factors affect plants (20 marks; KCSE 2004)

• a). Describe how gaseous exchange takes place in terrestrial plants (20 marks; KCSE2005)

b). How is the human eye adapted to its function? (20 marks; KCSE 2005)

• a). Describe how human kidney functions (20 marks; KCSE2006)

b).Describehowwatermovesfromthesoiltotheleavesinatree (20marks; KCSE2006)

• a). Describe the structure and functions of the various parts of the human ear (20 marks; KCSE 2007 )

b). Describe causes and methods of controlling water pollution (20 marks; KCSE 2007 )

• Describe the nitrogen cycle (20 marks; KCSE2008)
• a). State four characteristics of gaseous exchangesurfaces

b). Describe the mechanism of gaseous exchange in a mammal (16 marks; KCSE 2008)

• a). How are flowers adapted to wind and insect pollination? (20 marks; KCSE2009 )

b). Describe the role of the liver in homeostasis in the human body (20 marks; KCSE2009)

• a). Describe the process of fertilization in flowering plants (20 marks; KCSE2010)

b). Describe how a finned fish such as tilapia moves in water (20 marks; KCSE 2010)

• a). Describe the exoskeleton and its function in insects (13 marks; KCSE2011)

b). Describe how accommodation in the human eye is brought about when focusing on a near object (7 marks; KCSE 2011)

• Using a relevant example in each case, describe simple and conditional reflex action (20 marks; KCSE2012)
• a).Usingarelevantexample,describehowanallergicreactionoccursinahumanbeing

(10 marks; KCSE 2012)

b).Describehowenvironmentalfactorsincreasetherateoftranspirationinterrestrialplants

• a). Describe the process of blood clotting in human beings (10 marks; KCSE2013 )

b).Howarerespiratorysurfacesinmammalsadaptedtotheirfunctions? (10marks; KCSE 2013)

• Describe the role of the following organs in excretion andhomeostasis
• The liver (10 marks; KCSE2013)
• The skin during hot environmental conditions (10 marks; KCSE2013 )
• a). Explain how each of the following factors affect the rate ofphotosynthesis:
• Temperature (2 marks; KCSE2014)
• Chlorophyll concentration (2 marks; KCSE2014 )

b). Describe the process of carbohydrate digestion in human beings (16 marks; KCSE2014)

• a). How does excretion take place in plants (4 marks; KCSE2014)

b). Describe the role of the human skin in homeostasis (16 marks; KCSE 2014)

• a).Explainthevariouswaysinwhichseedsandfruitsareadaptedtodispersal (20marks; KCSE 2015)

b). How is a mammalian heart structurally adapted to its function? (20 marks; KCSE2015)

                                                                                                                                         2 | P a ge

• (a).Usingarelevantexampleineachcase,describesimpleandconditionalreflexaction

(20 marks; KCSE 2016)

b). Describe how the mammalian heart is structurally adapted to its function (20 marks; KCSE 2016)

• a ) Explain the importance of protecting the forest ecosystem with reference to the following (20 marks; KCSE 2017 )
• a) Climate change
• b) Biodiversity

c)Biotechnology

d)Water conservation

• e) Pollution
• b) Describe how a mammalian eye is structurally adapted to its functions (20 marks)
• a) Describe the mode reproduction in a named fungus (5 marks)
• b) Describe the roles of hormones in the menstrual cycle (15 marks; KCSE 2018 )
• a) Giving examples, describe the following among organisms (20marks; KCSE 2019 )
• Predator-prey relationship
• b) Explain the effect of increased physical activity on the following organ system (20 marks)
• a)(i)Explain the role of the liver in blood regulation (3 marks ; KCSE 2020)
• Describe how a mammalian heart is adapted to its functions (17 marks)
• b) (i) Explain how the presence of chloroplast in guard cell affect the opening of the stomata (5marks)

(ii) Describe how various environmental factors affect the rate of photosynthesis (15marks)

• a) (i) Explain the role of placenta during pregnancy(10 marks) ( KCSE 2021)
• ii) Explain features and mechanisms that hinder self pollination and self fertilization(10 marks)

b)( i) Describe how xylem is structurally adapted to its functions  (5marks)

(ii) Describe the functions of mammalian blood in the human body(15 marks)

• a i) Describe how plants eliminate waste products(8 marks; KCSE2022 )

ii)Describe the structure and function of mammalian nephron (12marks)

• b) i. Describe five tropic responses and their survival values (15marks)

ii)Describe how mammalian heartbeat is controlled                (5mks)

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KCSE 2023 Biology Essay Questions and Answers (KCSE 2023 Prediction Questions)

Here are KCSES 2022/2023 Biology Essay Questions and Answers (KCSE 2022 Prediction Questions). Content: 31 pages with 60 questions and answers.

BIOLOGY (231/2) Revision Questions (Essays): Expected Responses

Q1. Explain the various ways in which a typical cell is adapted to its functions

   Has a cell membrane; with pores; that regulates substances entering and leaving the cell; cytoplasm; contain sugars and salts; for maintaining its osmotic pressure; also has a liquid medium; for all biochemical reactions; nucleus; contain chromosomes having hereditary material; and controls all the activities of the cell; ribosomes; are sites for protein synthesis; golgi bodies/apparatus; for secretion of hormones and enzymes; formation of lysosomes; lysosomes; contain lytic enzymes for breaking down worn-out organelles; secretory vesicles; formed from golgi apparatus for secreting substances; smooth endoplasmic reticulum; synthesizes and transports lipids; rough endoplasmic reticulum; transport proteins; nucleolus; controls the activities of the nucleus; produces ribosomes; mitochondria; form sites for energy production; centrioles; formation of cilia and flagella; forms spindle fibres used in cell division; plant sap vacuoles; store salts and other dissolved substances; controls osmotic pressure and turgidity of cells; food vacuoles involved in digestion of engulfed food; chloroplasts; form sites for photosynthesis in plant cells;  Max. 20 mks

Q2. Explain how the various specialized cells are modified to carry out their functions in plants and animals

   Animal cells: Sperm cell; has acrosome containing lytic enzymes; that digest the egg membranes for penetration during fertilization; has a long tail; containing numerous mitochondria; to generate maximum energy for propulsion/swimming in the vaginal fluid after ejaculation; Red blood cells; are flattened, circular/spherical biconcave in shape; to increase the surface area for packaging of haemoglobin; has haemoglobin; that combines with respiratory gases; for transport to and from body tissues; White blood cells; are amoeboid in shape hence able to change shape; to engulf pathogens through phagocytosis; lymphocytes produce antibodies to fight pathogens; Nerve cell; has extensions/dentrites; to receive and send information for sensation; Ciliated epithelial cells; have cilia for propulsion of mucus that traps dust and micro-organisms in the respiratory tract; Muscle cells; elongated, striated and contractile; to bring about movement; Plant cells: Guard cells; bean-shaped; to regulate the size of the stomata allowing gaseous exchange; and control water loss; has chloroplasts with chlorophyll; for photosynthesis; Root hair cell; elongated; thin-walled; with dense cytoplasm for absorption of water and mineral salts; Epidermal cell; thin; for protection of inner tissues from mechanical and micro-organism attack; Palisade cell; contains numerous chloroplasts with chlorophyll; for photosynthesis; elongated; to increase surface area for trapping maximum amounts of light energy; Meristematic cell; thin-walled; with dense cytoplasm; for primary and secondary growth; Max. 20 mks

Q3. Describe how the mammalian body protects itself against infections

   Pathogenic microbes are found on the skin, respiratory tract, mouth, vagina and the intestinal tract; the skin; has a keratinised and waterproof cornified outer layer; that provides a mechanical barrier to microbes/prevents entry of microbes; sebaceous gland; produces sebum; which has antiseptic properties; the respiratory tract; produce mucus secretions that trap dust; cilia sweep/waft/propel the microbes to the pharynx for swallowing or to be coughed out; reflex actions of coughing/sneezing/vomiting help remove foreign materials from the respiratory tract/digestive tract; lysozymes/enzymes in saliva/nasal secretions/tears; digest walls of bacteria destroying them; gastric secretions such as hydrochloric acid lowers the pH in the stomach killing micro-organisms; clotting of blood; prevents entry of microbes after damage of blood vessels; phagocytosis; by phagocytes engulf and destroy microbes and other foreign bodies; lymphocytes are stimulated to produce antibodies; by proteins present in microbes protecting the body; antibodies destroy/kill micro-organisms through various ways: agglutinins; bind to pathogens making them clump together; killing them; Lysins; bind to pathogens and make them burst or disintegrate; opsonins; bind to pathogens making them easily recognized hence be engulfed/destroyed by other lymphocytes; anti-toxins; bind and neutralize toxins produced by micro-organisms; vagina is acidic; hence making it not conducive for growth and reproduction of micro-organisms; Max: 20 mks

Q4. How are the leaves of higher plants adapted to their functions?

    Broad and flattened lamina; to increase surface area; for absorption of light; thin blade; to reduce distance for diffusion of gases and penetration of light waves; transparent epidermis and cuticle; to allow light to penetrate to tissues; cuticle layer absent on stomata; to allow for gaseous exchange; one-cell thick epidermal layer; to reduce the distance over which sunlight penetrates; palisade cells have numerous chloroplasts containing chlorophyll; to trap maximum amounts of light energy; have stomata on the epidermis; to allow for gaseous exchange; and control of water loss through transpiration; palisade layer have elongated cells located at right angles to the leaf surface; for maximum absorption of light energy; spongy mesophyll; consists of spherical and loosely-packed cells; to create air spaces; which communicate with the atmosphere through stomata; for purposes of gaseous exchange and control of water loss; veins have conducting tissues: xylem; for movement of water and dissolved mineral salts; phloem; for translocation of manufactured food; Max. 20 mks

Q5.  Explain how the various teeth adapt mammals for nutrition

   Incisor; sharp; chisel-shaped; for biting; and cutting food; one root for support in the jaw bone; Canines; long; sharp; pointed; for holding prey; piercing; and tearing flesh from prey; single root; for support in the jaw bone; Premolars; large/wide; to increase surface area for grinding food; highly cusped; to increase surface area for grinding food; two roots; for firm support/anchorage in the jaw bone; molars; large/wide; to increase surface area for grinding food; highly cusped; to increase surface area for grinding food; Max. 20 mks

Q6. Describe what happens to a meal of oily beans and maize from the time of ingestion up to the time of absorption

   In the mouth; starch in maize; is digested by salivary amylase/ptyalin/diastase into maltose; food is chewed and mixed by teeth and the tongue; rolled into boluses by peristalsis; it enters into the stomach via the cardiac sphincter; in the stomach, gastric juice containing pepsinogen that is activated to pepsin; digests proteins in the beans; into shorter peptides; food is churned and allowed into the duodenum; via the pyloric sphincter muscle; in the duodenum; bile juice secreted by the gall bladder; emulsifies the oils in the beans into tiny oil droplets; pancreatic juice; secreted by the pancrease; contains pancreatic amylase; that digests starch to maltose; pancreatic lipase; that digests the oil in the beans to fatty acids and glycerol; trypsin; digests proteins into shorter peptides;  food enters into the ileum; where succus entericus is secreted; it contains maltase enzyme; that digests the maltose into glucose; that is absorbed; peptidase; digests peptides into amino acids; lipase digests the remaining lipids (oil) into fatty acids and glycerol; which is absorbed through the lacteals of the villi; Max. 20 mks

Q7. How are the small intestines in mammals adapted to their functions?

Small intestines consists of the duodenum and the ileum; most digestion of food occurs in the duodenum; bile from the gall bladder of the liver is secreted through the bile ducts; and it is used to emulsify fats/break fat particles into tiny droplets; to increase the surface area for enzyme action; the pancreas secretes pancreatic juice to the duodenum; the juice contains pancreatic amylase; that helps to breakdown the remaining starch into maltose; trypsin; (that is secreted in its inactive form, trypsinogen , and activated by enterokinase enzyme); hydrolyses proteins into shorter peptides; pancreatic lipase; converts lipids into fatty acids and glycerol; sodium hydrogen carbonate is also produced; to neutralize the acidic chyme from the stomach; and provide a suitable alkaline medium for pancreatic and other intestinal enzymes; the ileum is long; and narrow; to increase the surface area for complete digestion of food; and maximum absorption of digested food; highly-coiled; to reduce speed of food flow; for maximum digestion; and absorption; presence of villi; and microvilli; to increase surface area; for maximum absorption; dense network of capillaries; to transport blood; for efficient transport of absorbed food; presence of lacteals in the villi; for absorption of fatty acids and glycerol molecules; presence of enzymes: Lipase; for digestion of lipids into fatty acids and glycerol; maltase; for digestion of maltose to glucose molecules; peptidase; for breakdown of peptides into amino acids; sucrase; for digestion of sucrose into glucose and fructose; lactase; for digestion of lactose into glucose and galactose; goblet cells; produce mucus; to lubricate the walls of the ileum; for smooth flow of food; coats the walls of ileum to prevent digestion by peptidase enzyme; Max. 20 mks

Q8. Outline and explain the various homeostatic functions of the liver in mammals

   Deamination; process of removal of an amino group from an amino acid molecule; the process gets rid of excess amino acids in the body; as the body is not able to store them; the amino group enters the ornithine cycle; where it is combined with carbon (IV) oxideto form urea; which is excreted in urine through the kidney; Heat production; many metabolic activities take place in the liver; releasing heat energy; that is distributed by the blood to other parts of the body; this helps in thermoregulation; Storage of vitamins and mineral salts; Vitamins A, B, D, E and K; are stored in the liver; worn-out red blood cells, are broken down to yield iron; which is stored in the liver in form of ferritin; this is used later in case of shortage; Formation of red blood cells; occurs in the liver of the foetus; the liver also breaks down old/exhausted red blood cells; leading to formation of more in the bone marrow to replace the worn-out cells; to enhance oxygen and carbon (IV) oxide distribution; Regulation of blood sugar level; liver cells convert excess glucose into glycogen and fats under the influence of insulin hormone; the stored glycogen is however converted back to glucose; when glucose levels are low; by the liver cells; under the influence of glucagon hormone; Regulation of plasma proteins; plasma proteins such as prothrombin and fibrinogen are manufactured in the liver using the amino acids found in the liver; they play a major role in blood clotting; that prevents excessive blood loss and infection at the injured area; other plasma proteins produced by the liver such as serum and albumen; contribute to the maintenance of osmotic pressure in the body; non-essential amino acids are also synthesized by the liver; for use by the body; Storage of blood; the liver is highly vascularised; hence it is capable of holding a large volume of blood when the blood vessels dilate during hot conditions; when the temperatures are low, the blood vessels constrict under the influence of the endocrine and nervous systems; hence less blood is stored in the liver; this contributes to thermoregulation; Detoxification; this is the process where harmful compounds such as drugs and poisons; are converted to less toxic compounds in the liver; toxicity is caused by medication, drugs and microorganisms; the toxic compounds are later excreted in urine; detoxification prevents the accumulation of toxins in body cells; which could lead to death or malfunctioning of the body cells; Max. 20 mks

Q9. Explain why the following conditions are necessary for photosynthesis

• Carbon (IV) Oxide

Required in the dark stage of photosynthesis; it combines with the hydrogen ion from the light stage; to form glucose, proteins and lipids; low concentrations reduces the rate of production of energy and food; while high concentrations leads to an increase in the amount of energy and food formed;

It is used to break down water molecules (through photolysis); into hydrogen ions, oxygen and energy; the energy and hydrogen ions formed are used in the dark stage;

• Chlorophyll

Green pigment that traps light energy from the sun; that is used in photolysis of water molecules;

• Suitable temperature and pH

Temperature affects the enzymes involved in photosynthesis; suitable/optimum temperatures activate enzymes; for maximum production of food; while extremely low temperatures inactivate enzymes; leading to less or no production of food; high temperatures denature enzymes; stopping the process of photosynthesis; photosynthetic enzymes work well in low pH; so the rate is high; while higher pH reduces enzyme activity; lowering the rate of photosynthesis;

Forms a medium for the chemical reactions; it is split to yield hydrogen ions, oxygen and energy for use in the dark stage; solvent for the materials used in photosynthesis; Max. 20 mks

Q10. How is the ileum adapted to its functions?

      Long; and narrow; to increase the surface area for complete digestion of food; and maximum absorption of digested food; highly-coiled; to reduce speed of food flow; for maximum digestion; and absorption; presence of villi; and microvilli; to increase surface area; for maximum absorption; dense network of capillaries; to transport blood; for efficient transport of absorbed food; presence of lacteals; for absorption of fatty acids and glycerol molecules; presence of enzymes: Lipase; for digestion of lipids into fatty acids and glycerol; maltase; for digestion of maltose to glucose molecules; peptidase; for breakdown of peptides into amino acids; sucrase; for digestion of sucrose into glucose and fructose; lactase; for digestion of lactose into glucose and galactose; goblet cells; produce mucus; to lubricate the walls of the ileum; for smooth flow of food; coats the walls of ileum to prevent digestion by peptidase enzyme; Max. 20 mks

Q11. a) What is homeostasis?

         (Mechanisms of) control and maintenance of a constant internal environment regardless of the external conditions; 2 mks

• b) Name any three factors that must be maintained constant in mammalian bodies

          Temperature; Water; Salt or ion content; Carbon (IV) oxide; Glucose; amino acids; Max. 3 mks

• c) Explain how endotherms respond to heat and cold conditions in their environment

         Heat/hot conditions: Increased sweating; to lose heat through latent heat of vaporization; dilation of arterioles under the skin; to bring more blood to the skin surface to lose heat to the atmosphere; decreased body metabolism; to reduce heat generation; erector pili muscles relax; making hair follicles to relax hence hair lies flat on skin, no air is trapped; to lose heat; slow/reduced muscular activity due to slow metabolism; to reduce heat production; panting to expose tongue and mouth; to release heat; moving to shades to avoid direct heat; aestivation; to escape the extreme heat; flapping of ears to create currents to carry away heat; Cold conditions: stamping of feet; to generate heat; basking in the sun to gain heat directly; less production of sweat; to reduce water loss through latent heat of vaporization; vasoconstriction of arterioles; hence less blood flow to the skin surface to reduce heat loss; increased metabolism through release of more thyroxine hormone; to generate heat; erector pili muscles contract; pulling hair follicles hence hair is raised; to trap a layer of moist air; to prevent heat loss; shivering/rapid contraction of muscles; to yield heat to warm body; Max. 15 mks

Q12. Describe the route taken by water from the soil up to the evaporating surface of a plant

      Water is drawn into the root hair cells by osmosis; due to the presence of dissolved substances in the cell sap of root hairs, the concentration of cell sap is greater than that of the surrounding solution in the soil/concentration gradient; this exerts a higher osmotic pressure, thus drawing the water molecules across the cell wall and cell membrane into the root hair cells; more water drawn into the root hair cells dilutes the cell sap; making it less concentrated than that in the adjacent cortex cell of the root; due to osmotic gradient, water moves from the adjacent cells to the next by osmosis; until it enters the xylem vessels located in the center of the root; the xylem vessels of the root then conduct the water up into the xylem vessels in the stem into the leaves; there is a force in the roots which pushes water up the stem; this force is known as root pressure; and can be considerably high in some plants; energy from the endodermal cells of the root is responsible for driving this force; in the xylem vessels, water would rise up by capillarity; to some extent because the vessels are narrower and there is  a high attractive force between the water molecules and the cell walls; the cohesive; and adhesive forces are important in the maintenance of a continuous and uninterrupted water column in the xylem vessels up the tree to the leaves; water vaporizes from the spongy mesophyll cells; their cell sap becomes concentrated than the adjacent cells. This increases the osmotic pressure of the spongy mesophyll cells; as a result of this, water flows into the cell from other surrounding cell, which in turn takes in water from xylem vessels within the leaf veins; this creates a pull/suction force that pulls a stream of water from xylem vessels in the stem and roots. This force, known as transpiration pull; helps in maintaining a continuous column of water from the roots to the leaves; water flows from the midrib into leaf veins from where it enters leaf cells; from the mesophyll cells, it enters the airspaces; then the substomatal air chambers; from where it evaporates through the stomata; to the atmosphere; Max. 20 mks

Q13. How is the mammalian heart adapted to its functions?

Heart is enclosed in a pericardial membrane/pericardium; that produces a fluid; to lubricate it; the membrane also keeps the heart in position; It is covered in a fatty layer; that acts as a shock absorber; made up of cardiac muscles; which are interconnected/interacted hence contract and relax without fatigue or nervous stimulation/myogenic; for continuous pumping of blood throughout the lifespan of the animal; the muscles are supplied by nutrients and oxygen; by the coronary arteries; and the coronary veins take away wastes and carbon (IV) oxide; heart is divided into 4 chambers; for efficient double circulation/ avoid mixing of oxygenated and deoxygenated blood/carry large volume of blood; has interventricular septum; to separate oxygenated and deoxygenated blood; ventricles are thick/muscular; to generate high pressure to pump blood out of the heart; left ventricle has thick muscles/more muscular; to pump blood to all body tissues; heart has bicuspid; and tricuspid valves; to prevent back flow of blood to left auricle; and right auricle respectively; valves have tendinous cords/valve tendons; to prevent them from turning inside out; semi lunar valves located at the beginning of major arteries; prevent backflow of blood into the ventricles; has sino-artrio node located in the muscles of the right auricle; to initiate heart beat/contractions of heart muscles/cardiac muscles, rate of heart beat is controlled by nerves; vagus nerve; slows down heartbeat; while sympathetic nerve; speeds up the heartbeat; has aorta; to transport oxygenated blood to all body parts; has pulmonary artery; that transports deoxygenated blood from right ventricles to lungs for oxygenation; has pulmonary vein; that transports oxygenated blood from lungs to the left ventricles; for distribution to all body parts; has the venacava; that  receives deoxygenated blood from all body parts to right ventricles; Max. 20 mks

Q14. Describe double circulation in mammals

 Deoxygenated blood from body tissues (except lungs); enters the heart via the right auricle; through the venacava; it flows to the right ventricle; via the tricuspid valve; the right ventricle contracts; pumping blood; via the semi lunar valves; through the pulmonary artery; to the lungs for oxygenation; the oxygenated blood from the lungs; flow through the pulmonary vein; to the left auricle; via the bicuspid valve; to the left ventricle; the left ventricle contracts; pumping blood via the semi lunar valves; through the aorta; to the rest of the body tissues; Max. 20 mks

Q15. Describe the process of urine formation in the mammalian kidneys

      The afferent arteriole which is a branch of the renal artery supplies blood to the glomerulus; the afferent arteriole has a wider lumen/diameter than the efferent arteriole; which takes away blood from the glomerulus; the differences in the diameter of the afferent and the afferent vessels causes high pressure; leading to ultrafiltration of blood; the walls of the blood capillaries are one-cell thick; hence glucose, amino acids, vitamins, hormones, salts, creatine, urea and water filter into the Bowman’s capsule; to form glomerular filtrate; white blood cells, red blood cells, plasma proteins such as globulin and platelets are too large to pass through the capillary wall; hence remain in the blood capillaries; useful substances in the human body are selectively reabsorbed; back into the blood stream at the proximal convoluted tubule; the tubule is highly coiled; to increase the surface area for reabsorption of the substances; the useful substances include amino acids, glucose, vitamins, hormones, sodium chloride and water; many mitochondria found at the proximal convoluted tubule; provide energy for reabsorption of these substances against a concentration gradient; the glomerular filtrate flows into the descending and the ascending limb of the loop of Henle; blood in the capillaries and the glomerular filtrate in the loop of Henle move in opposite directions/counter-current flow; this provides a steep concentration gradient that leads to maximum absorption of water through osmosis; sodium chloride is actively absorbed from the ascending limb into the blood capillaries; under the influence of aldosterone hormone; the glomerular filtrate flows into the collecting tubule from where, more water is reabsorbed into the blood stream; antidiuretic hormone influences the amount of water to be reabsorbed depending on the osmotic pressure of the blood; the glomerular filtrate from several collecting tubules now referred to as urine; is emptied into the collecting duct; the urine passes through pyramid, pelvis and ureter into the bladder; where it is stored for some time. The sphincter on the urethra relaxes to allow urine to be released from the body; Max. 20 mks

Q16. Explain the role of the following hormones during homeostasis

• Antidiuretic Hormone (ADH)

Secreted by the (posterior lobe/end) pituitary gland; in response to an increase in the osmotic pressure of blood; the hormone stimulates the distal convoluted tubules and the collecting ducts; to increase their permeability to water; this increases the reabsorption of water into the bloodstream; concentrated and less urine is excreted; when the osmotic pressure decreases, less or no hormone is produced; hence the tubules become impermeable to water; less water is reabsorbed into the bloodstream; hence more dilute urine is excreted; fluctuations in the osmotic pressure is detected by the hypothalamus;

Secreted by the pancrease; in response to a rise in blood sugar level; it stimulates liver cells to convert the excess glucose into glycogen and fats for storage in the liver and muscle cells; increases the oxidation of glucose in respiration to yield water energy and carbon (IV) oxide/increases metabolism in the body; this leads to a fall in blood glucose to normal level;

Secreted by the pancrease; in response to a decline in blood glucose level; it stimulates liver cells to convert the stored glycogen and fats back to glucose; stimulates the conversion of amino acids to glucose; and stops the oxidation of glucose in the body cells; the glucose formed is released to the bloodsteream causing a rise of blood glucose level to normal; Max. 20 mks

Q17. a) Distinguish between Diabetes mellitus and Diabetes insipidus

            Diabetes mellitus is a condition/disease caused by failure of the pancrease to produce adequate insulin hormone; leading to excess glucose levels in the body some of which is released in urine while diabetes insipidus is a condition caused by failure/inability of the kidney tubules to control the amount of water in urine as a result of a defect in production of antidiuretic hormone (ADH) leading to production of more dilute urine; Max. 2 mks

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