South Sudan Secondary Biology 4 - Comprehensive Notes

South Sudan Secondary Biology 4 - Comprehensive Notes

General Information

• All courses in this secondary series were developed by the Ministry of General Education and Instruction, Republic of South Sudan.
• The books have been designed to meet the secondary school syllabus.
• The books equip students with skills to fit in the modern-day global society.
• Each year comprises a Student’s Book and a Teacher’s Guide.
• The Secondary Biology book has been written and developed by the Ministry of General Education and Instruction, Government of South Sudan in conjunction with subject matter experts.
• The course book will have a fun and practical approach to the subject of Biology.
• The book seeks to impart lifelong skills to the students.
• The book comprehensively covers the Secondary 4 syllabus as developed by the Ministry of General Education and Instruction.

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Republic of South Sudan, Ministry of General Education and Instruction

• ©2018, THE REPUBLIC OF SOUTH SUDAN, MINISTRY OF GENERAL EDUCATION AND INSTRUCTION. All rights reserved.
• No part of this book may be reproduced by any means graphic, electronic, mechanical, photocopying, taping, storage, and retrieval system without prior written permission of the Copyright Holder.
• Pictures, illustrations, and links to third-party websites are provided in good faith, for information and education purposes only.

Foreword

• Developed by the Ministry of General Education and Instruction based on the new South Sudan National Curriculum.
• National Curriculum is learner-centered to meet the needs and aspirations of the new nation.
  • Aims: (a) Good citizens; (b) successful lifelong learners; (c) creative, active, and productive individuals; and (d) Environmentally responsible members of our society.
• Textbook is designed to contribute to the achievement of these aims.
• Revised thoroughly by Subject Panels and deemed fit for the purpose.
• Approved for use in all schools of the Republic of South Sudan (except international schools), with effect from 4th February 2019.
• Gratitude expressed to various individuals and organizations for their support in the development of the National Curriculum and school textbooks.
• Intended to benefit the people of South Sudan, especially children and youth and future generations.
• Aims to enhance the quality of education in the country to promote peace, justice, liberty, and prosperity for all.
• Teachers urged to put the textbook to good use.

Contents

Unit 1: Biochemistry of Photosynthesis and Respiration

• 1.1 Necessity of Chlorophyll, Light Energy, and Carbon Dioxide for Photosynthesis
• 1.2 Limiting Factors for Photosynthesis
• 1.3 Internal Structure of the Leaf and its Adaptations to Photosynthesis
• 1.4 Importance of Photosynthesis
• 1.5 The Process of Photosynthesis
• 1.6 Chemical Compounds Which Constitute Living Organisms
• 1.7 Respiration
• 1.8 Respiratory System in Animals
• 1.9 Respiration in Other Animals
• 1.10 Gaseous Exchange in Human Beings and Plants
• 1.11 Gaseous Exchange in Plants

Unit 2: Reproduction and Growth in Plants and Animals

• 2.1 Asexual Reproduction in Lower Organisms
• 2.2 Asexual Reproduction in Plants
• 2.3 Structure of a Flower
• 2.4 Pollination
• 2.5 Fertilisation and Seed Formation
• 2.6 Fruits, Seed Dispersal, and Germination
• 2.7 Seed Dormancy
• 2.8 Reproduction
• 2.9 Sexual Reproduction in Animals
• 2.10 Sexual Reproduction in Human Beings
• 2.11 he Menstrual Cycle
• 2.12 Sex Hormones
• 2.13 Fertilisation and Implantation
• 2.14 Pregnancy, Ante-Natal Care, and Birth
• 2.15 Cell Division
• 2.16 Chromosomes
• 2.17 Mitosis
• 2.18 Meiosis
• 2.19 Growth and Development in Plants and Animals
• 2.20 Primary and Secondary Growth

Unit 3: Co-ordination in Plants and Animals

• 3.1 Co-ordination in Plants
• 3.2 Role of Auxin in Controlling Shoot Growth
• 3.3 Other Forms of Plant Responses
• 3.4 Co-ordination in Animals
• 3.5 Structure of the Nervous System in Vertebrates
• 3.6 Structure and Functions of Neurones
• 3.7 Relex Arcs and Relex Actions
• 3.8 Chemical Co-ordination in Animals and the Endocrine System

Unit 4: Homeostasis in Plants and Animals

• 4.1 Deinition of Homeostasis
• 4.2 he Role of Endocrine System in Homeostasis
• 4.3 Osmoregulation

Unit 5: Genetics and Inheritance

• 5.1 Inheritance and Key Terms Used in Genetics
• 5.2 Monohybrid Inheritance
• 5.3 Hybrid and Test Cross
• 5.4 Complete Dominance, Incomplete Dominance and Co-dominance
• 5.5 Genetic Material
• 5.6 Sex Determination in Humans Beings
• 5.7 Sex Linkage
• 5.8 Variations Among Organisms
• 5.9 Continuous and Discontinuous Variation
• 5.10 Mutations
• 5.11 Evolution
• 5.12 Genetic Engineering

Unit 6: Adaptation and Evolution

• 6.1 Meaning of Biological Evolution
• 6.2 heories About Origin of Life
• 6.3 Natural Selection
• 6.4 Convergent and Divergent Evolution
• 6.5 Evolutionary Processes That Lead to the Tree of Life
• 6.6 Natural Selection and Adaptation

Unit 7: Support and Movement in Plants and Animals

• 7.1 What is Support and Movement in Plants and Animals?
• 7.2 Support and Movement in Plants
• 7.3 Support and Movement in Animals
• 7.4 Mammalian Skeleton

Unit 1: Biochemistry of Photosynthesis and Respiration

• Learning outcomes:
  • Compare and contrast the biochemistry of photosynthesis and respiration.
  • Design and carry out practical investigations on aspects of photosynthesis and respiration.
  • Investigate practically the factors affecting rates of photosynthesis.
  • Investigate practically leaf structure to understand how gases are exchanged.
  • Appreciate the importance of biochemical processes in photosynthesis and respiration in the carbon cycle.
  • Value the importance of essential elements in supporting life processes.
• Introduction: This unit explores the biochemistry of photosynthesis in plants and respiration in both plants and animals.

Photorespiration

• Plants manufacture their own food through photosynthesis.
• Carbon (IV) oxide combines with oxygen in the presence of sunlight to form glucose and oxygen.
• Equation:
  $6CO<em>2 + 6H</em>2O ounderline{Light energy \ chlorophyll} C<em>6H</em>{12}O<em>6 + 6O</em>2$
  (Carbon IV oxide) (Water) (Carbohydrate i.e. glucose) + Oxygen
• Chlorophyll traps light energy from the sun.
• Oxygen is given off as a by-product.
• Respiration is the process through which chemical energy present in organic molecules is released through oxidation.
• Respiration takes place in both plants and animals.
• Glucose is oxidised in the presence of oxygen to form carbon (IV) oxide, water, and energy in the form of ATP.
• The general equation is as follows:
  $C<em>6H</em>{12}O<em>6 + O</em>2 ounderline{} 6CO<em>2 + H</em>2O + 38ATP$
  (Glucose) (Oxygen) (Carbon IV oxide) (Water) (Energy)

Activity 1.1: Testing for the Presence of Starch in Leaves

• Change in color of iodine solution from brown to blue-black indicates the presence of starch.
• This means that the part of the leaf tested has starch and therefore photosynthesis must have taken place in that part.
• For photosynthesis to take place, certain conditions are necessary:
  • Light energy
  • Carbon dioxide
  • Water
  • Chlorophyll

Activity 1.2: To Investigate Necessity

• Procedure: Design an experiment which shows chlorophyll is necessary for photosynthesis.
• A variegated leaf is one whose surface shows two colors, for example green on some parts and white on others.
• The green part of the leaf has cells with chlorophyll. Therefore photosynthesis will take place and form starch.
• Starch present in this part will turn iodine from brown to a blue-black color.
• The yellow part has cells that do not contain chlorophyll. These cells will not carry out photosynthesis; therefore no starch will be formed.
• The starch test will be negative.
• The green part of the leaf acts as a control experiment because it has all the conditions required for photosynthesis.

Activity 1.3: To Investigate Necessity of Light in Photosynthesis

• The leaf turns blue-black except in the covered region when tested with iodine solution.
• This covered region did not receive light hence photosynthesis did not occur resulting in absence of starch in this region.
• The uncovered region received sunlight and starch was formed there due to photosynthesis.
• Photosynthesis involves the synthesis of organic food substances by plants.
• The overall photosynthesis equation is:
  $Water + carbon dioxide ounderline{Light \ energy \ chlorophyll} glucose + oxygen$
  $6CO<em>2(g)+ 6H</em>2O(l) ounderline{sunlight \ chlorophyll} C<em>6H</em>{12}O<em>6(s) + 6 O</em>2 (g)$

End products of photosynthesis

• Glucose: Main product. Used in respiration to release energy. Excess glucose is stored as starch or oil.
• Oxygen: Some of the oxygen is used during respiration while the rest is released to the atmosphere during gaseous exchange.

Activity 1.4: To Show That Oxygen is Produced During Photosynthesis

• After some time, bubbles will be seen coming out from the water weed plants used.
• In presence of sunlight, photosynthesis takes place producing oxygen as a by-product.
• Oxygen relights a glowing splint.
• In darkness, no photosynthesis takes place.
• The set-up in the dark cupboard therefore does not produce any oxygen.

Check your progress 1.1

1. Below is an incomplete symbolic equation of photosynthesis. $carbon dioxide + Water + X ounderline{Y \ sunlight}glucose + oxygen$
   • (a) What does Y represent?
     • Chlorophyll
   • (b) What is product X?
     • Glucose
2. The figure below shows an experiment that was carried out on two green leaves. The mid-rib of leaf M was severed at point x while still attached to the tree in an evening of a sunny day. The mid-rib of leaf N was left intact. The two leaves were detached from the plant and tested for starch.
   • (a) Account for the distribution of starch in part of leaf M.
     • The distribution of starch in leaf M indicates that photosynthesis occurred in the green parts of the leaf where chlorophyll was present, as these parts received sunlight and were able to produce starch.
     • Point X was severed. The interruption of water transport means starch cannot form.
   • (b) There was complete absence of starch in leaf N. Account for this.
     • The complete absence of starch in leaf N might be due to the experiment being conducted in the mid-evening, leading to a lack of sufficient light for photosynthesis to occur effectively even though water transport was unhindered.

1.2 Limiting factors of photosynthesis

• A limiting factor is a variable which limits the rate of photosynthesis.
• Photosynthesis may be limited by a shortage in supply of one or more raw materials or other factors necessary for photosynthesis.

a) Light intensity

• In darkness, plants cannot carry out photosynthesis at all.
• In low light intensity, the rate of photosynthesis is low.
• As light intensity increases, the rate of photosynthesis also increases.
• There reaches a point where the plant cannot photosynthesise any faster even with further increase in light intensity.
• At this point, any other factor affecting the rate of photosynthesis hinders the rate of photosynthesis.

b) Carbon dioxide concentration

• The amount of carbon dioxide in the atmosphere is quite low (0.03%). Therefore it can also be a limiting factor to photosynthesis.
• Increase in carbon dioxide increases the rate of photosynthesis.
• But this continues only to a certain point where rate of photosynthesis does not increase further with more carbon dioxide since other factors affecting photosynthesis become limiting.
• AB: Increase in concentration of carbon dioxide causes a rise in rate of photosynthesis.
• BC: Limiting factors set in and a further rise in carbon dioxide concentration does not cause a corresponding increase in rate of photosynthesis.

c) Temperature

• Photosynthesis is an enzyme- catalysed reaction and is therefore affected by temperature.
• If temperatures are low, plants photosynthesise very slowly, but as temperature increases, the rate of photosynthesis also increases.
• Rate of photosynthesis is highest at optimum temperature.
• Further increase in temperature above optimum results to a decrease in rate of photosynthesis since enzymes are denatured.
• AB – Increase in temperature causes a corresponding increase in the rate of photosynthesis. The rate of photosynthesis is highest at B.
• BC – Any further increase in temperature denatures the enzymes. Therefore the rate of photosynthesis declines.

d) Water

• Only about 1% of the water taken in by plants is used for photosynthesis.
• Water shortage only indirectly affects the rate of photosynthesis, for instance, when water is in short supply, the stomata close.
• This lowers the exchange of gases between the leaf and the atmosphere. As a result, less carbon dioxide diffuses via the stomata into the leaf.
• This reduces the rate of photosynthesis.

Check your progress 1.2

1. Which of the following is not a limiting factor in photosynthesis?
   • A. Amount of oxygen
2. The graph below shows the effect of increasing carbon dioxide on the rate of photosynthesis.
   • Explain why the rate of photosynthesis does not continue to increase with increase in carbon dioxide concentration.
     • At a certain point, other factors such as light intensity, temperature, water availability, or chlorophyll concentration become limiting, and increasing the carbon dioxide concentration further will not increase the rate of photosynthesis any longer.
3. Temperature is a factor that limits the rate of photosynthesis. Explain why the rate of photosynthesis starts to decrease as temperature increases beyond 40oC and eventually stops beyond 60oC.
   • Beyond 40°C, the enzymes involved in photosynthesis begin to denature, losing their specific shape and function, thus slowing down the reaction. By 60°C, the enzymes are completely denatured, and photosynthesis stops entirely.
4. The atmospheric air contains 0.03% carbon dioxide. What will happen to the rate of photosynthesis if carbon dioxide level rises to 4%?
   • Initially, increasing the carbon dioxide level to 4% would increase the rate of photosynthesis. Eventually, limiting factor sets in, causing no increase in rate of photosynthesis.

1.3 Internal structure of the leaf and its adaptations to photosynthesis

• The leaf is the main organ for photosynthesis. However, other green parts of the plant carry out photosynthesis as well.
• The leaf has a cuticle which covers both upper and lower surfaces of the leaf. Immediately after the cuticle is the upper and lower epidermis respectively.
• The palisade mesophyll which contains palisade cells that carry out photosynthesis is located below the upper epidermis.
• It is followed by the spongy mesophyll which has cells with large air spaces between them.
• On the lower epidermis are tiny openings called stomata. They are surrounded by special cells known as guard cells.

Adaptations of the leaf to photosynthesis:

• The leaf blade is broad and flat to provide a large surface area for absorption of sunlight and carbon dioxide.
• Most leaves are thin. This reduces the distance across which carbon dioxide has to diffuse from the stomata to reach the photosynthesizing cells.
• Leaves have vascular bundles (xylem and phloem) which supply the cells with water and mineral salts, and transport manufactured food to the other parts of the plant.
• The leaf cuticle and epidermis are transparent and thin to allow easy penetration of light.
• Presence of stomata on the leaves allows easy diffusion of carbon dioxide.
• The leaves are well arranged to avoid overlapping and overshadowing. This ensures maximum exposure to light.
• The spongy mesophyll layer has cells that are irregular in shape and are loosely arranged hence have large air spaces between them. This allows gases to circulate freely thereby enhancing gaseous exchange between the cells and the air surrounding them.
• Palisade cells are closely packed, elongated, lie at right angles to each other, and contain many chloroplasts hence absorb maximum sunlight required for photosynthesis.

Check your progress 1.3

1. Use the diagram of the cross-section through the leaf to answer the questions that follow.
   • (a) Indicate on the diagram the following: guard cells, spongy mesophyll layer, palisade layer, and vascular bundles.
   • (b) Which cell type absorbs most carbon dioxide during the day?
     • Palisade cells
   • (c) State the role of the part labeled D in photosynthesis.
     • Vascular bundles (Veins): They transport water and mineral salts to the leaf for photosynthesis and carry away the products of photosynthesis (sugars) to other parts of the plant.
   • (d) Describe ways in which cell type B are suited for photosynthesis.
     • B (Palisade mesophyll cells): They are closely packed, contain many chloroplasts, and are located near the upper surface to maximize light absorption.
   • (e) Of what importance is the shape of cell type C in photosynthesis?
     • C (Spongy mesophyll cells): Their irregular shape and loose arrangement with large air spaces facilitate gas exchange (CO2 intake and O2 release) within the leaf.
2. The bar chart below shows the average number of chloroplasts in the different types of cells in a leaf.
   • Identify the cell types A, B, and C.
     • Cell type A: Palisade cells
     • Cell type B: Spongy mesophyll cells
     • Cell type C: Epidermal cells
3. Differentiate between the following:
   • (a) Epidermal cell and guard cell.
     • Epidermal Cells: They are generally transparent and do not contain chloroplasts, and they cover the leaf surfaces for protection with a waxy cuticle to prevent water loss.
     • Guard Cells: They contain chloroplasts, and they surround the stomata, controlling their opening and closing to regulate gas exchange and water loss.
   • (b) Palisade layer and spongy layer.
     • Palisade Layer: Located just below the upper epidermis, it consists of closely packed, elongated cells rich in chloroplasts, optimized for light capture.
     • Spongy Layer: Located below the palisade layer, its cells are loosely arranged with large air spaces between them, facilitating gas exchange.
       Explain the role of vascular bundles in photosynthesis.

1.4 Importance of photosynthesis

Activity 1.8

• Discuss with a friend the following questions:
  • (a) How would life be on earth without photosynthesis?
    • Without photosynthesis, there would be no plants, the base of most food chains. Animals would have no food; therefore, there would be no animal life. Therefore, there would be no cycle of life on earth.
  • (b) What do you think are the importance of photosynthesis?
    • Photosynthesis synthesizes chemical energy, reduces atmospheric carbon dioxide, produces oxygen, and allows for the continuation of life on earth in the way we know it.
• Share your findings with the class.

Class Activity: Debate

• Organise a class debate with a motion: Deforestation is the main cause of global warming.

Check your progress 1.4

1. Describe the role of plants in an ecosystem.
   • Plants are primary producers, converting light energy into chemical energy through photosynthesis, forming the base of the food chain and fixing carbon dioxide.
2. Suggest conservation methods you can initiate in your village to prevent environmental degradation
   • Reforestation, waste management, sustainable farming, and advocating for environmental protection in schools and communities can help prevent environmental degradation.

1.5 The process of photosynthesis

• Photosynthesis occurs through a series of chemical reactions.
• These reactions can be divided into two main stages.
• The first stage requires light energy and is called the light stage.
• The second stage does not require light energy and is called the dark stage or the light independent stage.

The light stage

• It takes place in the grana of the chloroplast.
• During this stage, chlorophyll absorbs light energy. This energy is used in two ways.
• (i) Some is used to split up water molecules into hydrogen ions and oxygen. This is known as photolysis of water.
  2H2O 4H+ + O2
  water hydrogen ions oxygen
• (ii) Some of the absorbed sunlight energy is converted to ATP.
• ATP (Adenosine triphosphate) is a high energy compound consisting of an adenosine molecule bonded to three phosphate groups. It is present in all living tissues.

he Breakage of One Phosphate

• he Breakage of One Phosphate (energy-rich bond) linkage to form ADP (adenosine diphosphate) provides energy for physiological processes such as muscular contractions.

The dark stage

• The dark stage takes place in the stroma at the same time that the light stage is taking place in the grana.
• Carbon dioxide diffuses into the stroma from the cell cytoplasm.
• The hydrogen from the light stage combines with carbon dioxide to form glucose.
• This process uses the energy stored during the light stage and also requires enzymes.
• The manufacture of a carbohydrate (glucose) from carbon dioxide is called carbon dioxide fixation.

$CO<em>2 + 4H^+ ounderline{} (CHO)</em>2 + H_2O$
Carbon hydrogen simple sugar water
dioxide ions (glucose)

1.6 Chemical compounds which constitute living organisms

• All living things are made up of chemical compounds.
• Some of these are described as organic compounds. These are complex compounds which contain mainly carbon, hydrogen and oxygen. A few organic compounds also contain phosphorus, sulphur and nitrogen.
• Examples of organic compounds are carbohydrates, lipids, proteins, and vitamins.
• Other compounds found in living organisms are described as inorganic. These are simple in structure. Examples are mineral salts, water, acids and bases.
• Both organic and inorganic compounds are important in the structure and function of cells.

(a) Carbohydrates

• These are chemical compounds made up of the elements carbon, hydrogen, and oxygen. Their general formula is $(CH<em>2O)</em>n$.
• Common examples of carbohydrates are sugars and starch. Carbohydrates are classified into three main groups:
  • Monosaccharides
  • Disaccharides
  • Polysaccharides

(i) Monosaccharides

• A monosaccharide is a single sugar unit.

• The general formula of a monosaccharide is $(CH<em>2O)</em>n$ where n can be 3, 5, or 6.

• Some examples of monosaccharides are glucose, fructose, and galactose.

  • Glucose is found in cell cytoplasm and blood of vertebrates.
  • Fructose is found in ripe fruits.
  • Galactose is found in milk.

• Structure of glucose:
  CH_2OH\ \ \ \OH \ H \ H \ \ H \ \HO \OH

• Structure of fructose:
  CH2OH\ \ \ HO \ CH2OH \ \OH \HO \ H \ O \ \ H

• Structure of galactose:
  CH_2OH\ \ \ HO \OH\ \OH\ \OH\ \ \ H \ H \ H \ \H\ \ O

(ii) Disaccharides

• A disaccharide is a double sugar formed when two monosaccharide molecules combine.

• The chemical process that forms a disaccharide from the two monosaccharides is called a condensation reaction.

• In this process, a water molecule is formed and released.

• Disaccharides are soluble in water and taste sweet.

• Example:
  $monosaccharide + monosaccharide ounderline{condensation} disaccharide + water$
  $C<em>6H</em>{12}O<em>6 + C</em>6H<em>{12}O</em>6 ounderline{Condensation \ Hydrolysis (dissacharides)} C<em>{12}H</em>{22}O<em>{11} + H</em>2O$

• Condensation is a reversible reaction. The disaccharide can be split by the addition of water to form two monosaccharides. This chemical reaction is called hydrolysis.

Some common examples of disaccharides

• Sucrose (cane sugar) is present in green plants and extracted from sugarcane and sugar beet.

• Maltose (malt sugar) is in germinating barley.

• Lactose (milk sugar) is in the milk of all mammals. When the two monosaccharide molecules combine.

• 1. glucose + glucose → maltose + water

• 2. glucose + galactose → lactose + water

• 3. glucose + fructose → sucrose + water

(iii) Polysaccharides

• A polysaccharide is a large complex carbohydrate molecule formed when many monosaccharide molecules link up in condensation reactions.

• The hydrolysis of a polysaccharide therefore gives rise to many monosaccharide units.

• Some common examples of polysaccharides are starch, cellulose and glycogen.

(a) Starch

• Starch is the storage form of glucose in plants. Each starch molecule has about 300 - 1000 glucose units. Most starch in plants can be found in seeds and storage organs like potato tubers. It gives a blue- black colour with iodine in potassium iodide solutions. This is the laboratory test for starch.

CH2OH \\H \OH \OH \ H \\H \OH\ H \\O \ \H \H\ \ \O ounderline 6\CH2 \OH \\OH \OH \\H \ H \ \H \\ O \ \H \H\ \ \O\ \Reducing \end \Branch \point

(b) Glycogen

• Glycogen is the main storage form of glucose in animals. It is made up of about 30,000 glucose molecules. Large amounts of glycogen are found in the liver. It is also found in muscles attached to the skeleton. Fungi also store carbohydrate in form of glycogen.
• Structure of glycogen

CH2OH\ \\ OH \OH \ H\ \H\ \\O\ CH2OH\ \ \\ OH \OH\ \H\ \ HO\ \ \\ OH\Reducing\end \end \Branch \point\ a \ (1 \6) linkage\ a \ (1 \6) linkage

(c) Cellulose

• A molecule of cellulose may have as many as 14,000 glucose units. It is the most abundant of all molecules found in plants. It is found as the major part of the structure of cell walls in plants.
• Wood is largely made up of cellulose and other substances. Cotton is almost purely made of cellulose. Cellulose is fibrous, tough and insoluble in water.
• Because of its fibrous nature, it is used by man to make cotton goods. It is also used to make paper.
  *Structure of cellulose:

(b) Proteins

• Proteins are complex compounds.
• hey too are made up of the elements carbon, hydrogen and oxygen. In addition, they have nitrogen. Some proteins may also contain sulphur or phosphorus.
• hese elements make up units called amino acids.
• Amino acids are the building units of proteins.
• here are about twenty diferent types of amino acids which occur naturally in plants and animals.
• hese amino acids combine diferently in a chain to form diferent types of proteins.
• here exists a large variety of proteins.

Summary of the General Structure of an Amino Acid Moleule

Hydrogen Carbon Carboxyl Group Amino Group

Peptides Peptides are molecules formed when a few amino acids combine.
*When two amino acid molecules combine, they form a dipeptide. his process is a condensation reaction which involves the removal of a water molecule.
*Condensation is a reversible reaction. his means that it is possible to get back the substances which we began the reaction with. he reverse process is called hydrolysis. Dipeptide. Condensation Hydrolysis Peptides
*If three amino acids combine by condensation, the compound formed is called a tripeptide.
*When a large number of amino acids combine by condensation, then the new molecule formed is very large. It is called a polypeptide. he word poly means many. Polypeptide molecules are also called protein molecules.
*amino acid + amino acid + amino acid → protein + water
*Properties of Proteins
*hey form large complex structures which are insoluble in water.
*High temperatures and extreme pH permanently alter their chemical structure and make them functionless (denatured).

(c) Lipids

• Lipids are fats and oils.
• he elements found in lipids are the same as those in carbohydrates, namely carbon, hydrogen and oxygen.
• However, lipids have much fewer oxygen atoms than hydrogen atoms compared with carbohydrates.
• Fats are lipids commonly found in animal tissue. An exception is the whale which has oil.
• Oils are lipids commonly found in plants. he building units in a lipid molecule are fatty acids and glycerol.
• One glycerol molecule combines with three fatty acid molecules in a condensation reaction to form a lipid known as a triglyceride.
• hree water molecules are given out. his reaction can be reversed by hydrolysis where the triglyceride (lipid) is split to glycerol and three fatty acid molecules.

Breakdown Summary:

glycerol + fatty acid → fatty acid → fatty acid ounderline{condensation\hydrolysis} + 3 \ water \ molecules → Lipid

A B
Look at the illustrations above. What makes plants grow? How do the plants make their food for growth? How does respiration take place in both plants and animals? What are the end products of respiration? What do letters A, B, C and D represent?

Respitaton is described as a food's oxidization to liberate energy.

• Overall respiration involves two processes:
  • It is a stepwise oxidation of complex organic molecules and release of energy as ATP for various cellular metabolic activities.
  • The plants obtain oxygen from their environment and return carbon dioxide and water vapor into it. This mere exchange of gases is known as external respiration or breathing in the case of animals. It is a physical process.

*The biochemical process, which occurs within cells and oxidises food to obtain energy, is known as cellular respiration.

Kinds of respiration

• here are two kinds of respiration depending on whether oxygen is required or not.
• Respiration that requires oxygen in order to take place is known as aerobic respiration.
• Anaerobic respiration takes place in the absence of oxygen.
• The irst steps of both aerobic and anaerobic respiration are the same. hey involve splitting glucose into pyruvic acid.
• This process is known as glycolysis, which means sugar-splitting (usually one molecule of glucose is split into two molecules of pyruvic acid).
• It takes place in the cytoplasm and does not require the presence of oxygen.
• Only 2 ATPs of energy are produced during this process.

Aerobic respiration

• Aerobic respiration occurs when glucose is broken down in the presence of oxygen. A lot of energy (many ATP molecules) is produced.
• It occurs in all higher forms (organisms). In this type, oxygen is necessary. Aerobic respiration is summarised in the equation below.
• There are three stages in aerobic respiration, namely: A) glycolysis (b) the Krebs cycle c) oxidative phosphorylation
• Study stages of aerobic respiration questions.

C6H{12}O6 + 6O2 ounderline{} 6CO2 + 6H2O + 2880 \K joule

a) Glycolysis: his occurs in the cytoplasm of the cell. Glucose is broken down into pyruvic acid and energy-rich hydrogens are given of. he hydrogens move into the mitochondria to be used in oxidative phosphorylation. wo ATP molecules are produced during glycolysis.

b) Krebs Cycle breaks down the pyruvic acid completely into energy-rich hydrogens and carbon dioxide. he hydrogens will be used in oxidative phosphorylation and the carbon dioxide will be breathed out.

he Krebs cycle is the second stage of cellular respiration. During the Krebs cycle, energy stored in pyruvate is transferred to NADH and FADH2, and some ATP is produced.

Steps of the Krebs cycle:

• Before the Krebs cycle begins, pyruvic acid, which has three carbon atoms, is split and combined with an enzyme known as CoA, which stands for coenzyme A.
• he product of this reaction is a two-carbon molecule called acetyl-CoA. he third carbon from pyruvic acid combines with oxygen to form carbon dioxide, which is released as a waste product. High-