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PREFACE N-Level Science Biology Examination Notes is specially compiled to help pupils prepare for their GCE N-Level Biology Examination. This book follows closely the current syllabus. Biology notes are presented in point form for ease of understanding and systematic learning. Clearly illustrated diagrams and tables are also included to help students understand difficult processes. The author believes that students will find this book a good source of relevant and important notes and a useful revision guide and study aid. A.B. Terence B.Sc., M.Ed., PGDE CONTENTS CHAPTER 1: CELL STRUCTURE & ORGANISATION 1 1.1 Plant & Animal Cells 1.2 Specialised Cells, Tissues & Organs CHAPTER 2: DIFFUSION & OSMOSIS 6 2.1 Diffusion 2.2 Osmosis CHAPTER 3: ENZYMES 10 3.1 Enzyme Action 3.2 Effects of Temperature & pH on Enzyme Activity CHAPTER 4: BIOLOGICAL MOLECULES 14 4.1 Nutrients CHAPTER 5: ANIMAL NUTRITION 20 5.1 Human Alimentary Canal 5.2 Chemical Digestion CHAPTER 6: PLANT NUTRITION 28 6.1 Photosynthesis 6.2 Leaf Structure CHAPTER 7: TRANSPORT IN FLOWERING PLANTS 35 7.1 Vascular Tissue 7.2 Water & Ion Uptake 7.3 Transpiration & Translocation CHAPTER 8: TRANSPORT IN HUMANS 8.1 8.2 8.3 8.4 8.5 42 The Human Circulatory System The Heart The Blood Tissue Arteries, Veins & Capillaries. Coronary Heart Disease CHAPTER 9: RESPIRATION 9.1 Aerobic Respiration 9.2 Anaerobic Respiration 9.3 Human Gaseous Exchange 52 CHAPTER 10: 10.1 10.2 10.3 10.4 REPRODUCTION IN PLANTS Asexual Reproduction Sexual Reproduction in Plants Pollination Fertilisation CHAPTER 11: SEXUAL REPRODUCTION IN HUMAN BEINGS 11.1 11.2 11.3 11.4 11.5 11.6 57 Male Reproductive System Female Reproductive System Differences between Male & Female Gametes Menstrual Cycle Fertilisation & Development of the Zygote Sexually Transmitted Disease 61 CHAPTER 1 CELL STRUCTURE & ORGANISATION 1.1 Plant & Animal Cells 1. The cell is the structural, functional and biological unit of every living organism. It is literally the basic unit of life. 2. Figure 1.0 illustrates a typical (a) animal cell and (b) plant cell. smooth endoplasmic reticulum rough cell surface endoplasmic membrane reticulum nucleus cell wall cell surface membrane tonoplast centriole free ribosome vacuole vacuole Golgi body Golgi body vesicle mitochondrion chloroplast cytoplasm mitochondrion (b) Plant cell (a) Animal cell Figure 1.0 (a) animal cell and (b) plant cell 3. The important structures and organelles covered in the current syllabus are described below in alphabetical order: Cell Wall - Found only in plants, the cell wall is made of cellulose (a polysaccharide). - It is found just outside the cell membrane and is permeable to most substances. - It forms a rigid outer boundary and confers plant cells their unique shapes. - Main function is to provide support and protection for the plant cell. 1 CHAPTER 1 Centriole - Exists as a pair near the nucleus. - Plays a part in the separation of chromosomes during cell division. Chloroplast - Organelles that can capture energy from sunlight and combine carbon dioxide and water to form glucose in a process called photosynthesis. - Contains the green pigment chlorophyll. Chromatin - Consists of deoxyribonucleic acid (DNA) bound to proteins (found in the nucleus). - During cell division, chromatin condenses to form distinct threadlike structures called chromosomes. Cytoplasm - Can be in a liquid (sol) state or semi-solid (gel) state. - The site for most of the chemical activities of the cell. Mitochondrion (pl. mitochondria) - Oblong shaped organelle found in the cytoplasm of every eukaryotic cell. - Converts oxygen and nutrients into energy through cellular respiration. Nucleus - Coordinates the cell’s activities, which include growth, metabolic reactions, protein synthesis, and reproduction (cell division). - Stores the cell’s hereditary material, or DNA. - It consists of a nuclear envelope which encloses the nucleoplasm and DNA. Plasma Membrane (also called cell surface membrane) - It is a lipid bilayer and may have proteins embedded in it. - It is a partially permeable membrane. - Thus, it regulates what enters and leaves the cell and also provides protection and support. 2 CHAPTER 1 Protoplasm - It consists of the plasma membrane, cytoplasm and nucleus. - It consists of about 70% to 90% water with dissolved substances like mineral salts and organic compounds. The exact composition varies for different cells. Ribosomes - Involved in protein synthesis. - Found freely in the cytoplasm or attached to the surface of the rough endoplasmic reticulum. - Ribosomes found free in the cytoplasm make proteins used within the cell. - Ribosomes attached to the RER make proteins that will be transported out of the cell. Vacuole - Structure used to store materials like water, salts, proteins and carbohydrates. - In animal cells, the vacuoles are small and numerous. - In plant cells, the vacuole is usually a larger structure consisting of a tonoplast (membrane) enclosing a fluid known as cell sap. Differences between Animal and Plant Cells Animal Plant 1 Animal cells have small numerous vacuoles. Plant cells have a large central vacuole. 2 Animal cells have centrioles. Plant cells do not have centrioles. 3 Animal cells do not have a cell wall. Plant cells have a cellulose cell wall. 4 Animal cells no not have chloroplasts. Plant cells have chloroplasts. 1.2 Specialised Cells, Tissues & Organs Cell Differentiation Root Hair Cell (Figure 1.1) Structure - Root hairs are formed by extensions of the cell wall of the epidermal cells. - Mature root hair cells have a large central vacuole. - The cell wall of a root hair cell is thin to allow the easy uptake of water and dissolved salts. 3 CHAPTER 1 Function - Root hair cells greatly increase the area of the root which is exposed to the soil and through which water and dissolved nutrients can be absorbed. The larger surface area increases the effective rate of water and nutrient absorption. root hair cell wall nucleus plasma membrane tonoplast vcacuole Figure 1.1 A root hair cell Xylem Vessel (Figure 1.2) Structure - Xylem vessels are dead at maturity. - They have thick lignified secondary cell walls which prevent the cells from collapsing under the negative pressure under which xylem tissue functions. - They form continuous hollow structures that allow easy movement of water and mineral salts. - They also provide strength and support for the plant. Function - Xylem transports water and dissolved mineral salts upwards in the plant from the roots towards the stem and leaves. Figure 1.2 Xylem vessels with pitted lignified walls. Red Blood Cell (Erythrocyte) (Figure 1.3) Structure - Red blood cells do not have a nucleus and are biconcave in shape. - The lack of a nucleus allows more room for haemoglobin; a protein that helps transport oxygen. 4 CHAPTER 1 - The biconcave shape increases the surface area to volume ratio to increase the rate of uptake and release of oxygen through diffusion. Function - Transport oxygen Depressed centre due to the lack of a nucleus. Figure 1.3 Red blood cells (erythrocytes) Cellular Organisation 1. In a multicellular organism, cells are grouped together at different levels of complexity to carry out specific functions. This type of organisation allows the organism to coordinate and carry out different functions efficiently and effectively. 2. The different levels of cellular organisation can be categorised as: cells form tissue organ form Tissue: form organ system Cells of the same type grouped together to carry out a specific function. e.g. cardiac tissue, muscle tissue, connective tissue Organ: Different tissues work together to carry out a specific function. e.g. The heart is made of cardiac muscle tissue, elastic tissue, nervous tissue and connective tissue which together help it to pump blood. Organ System: Several organs working together to carry out a specific function. e.g. digestive system; respiratory system; nervous system 5 CHAPTER 1