Download N Level Science Biology Examination Notes

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
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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.
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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.
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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.
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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.
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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
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CHAPTER 1