Biology N.M.

Narine
Digestion

Digestion is the breakdown of complex food substances into simpler food substances.

Types of digestion:

 Mechanical digestion – physical breakdown of food which occurs mainly in the mouth and stomach.
 Chemical digestion – chemical breakdown of food which occurs in the mouth, stomach, duodenum and
ileum.

Types of teeth and their function:

 Incisors – chisel shaped and used for cutting. 8

 Canine – pointed and used for tearing meat. 4
 Premolars – flat and rigid and used for grinding. 8
 Molars – flat and rigid and used for grinding. 12

Structure and function of a tooth

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Digestion

Structure and function of digestive system

Diagram of Digestive system

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Digestion

Enzymes

An enzyme is a biological catalyst. A catalyst is a molecule that speeds up the rate of a chemical reaction.
Enzymes convert substrates into products.

Properties of Enzymes

 All enzymes are proteins

 Enzymes are not chemically changed at the end of a reaction
 Enzymes are specific
 Work best at a certain pH
 Denatured at high temperatures
 Sensitive to poisons

pH scale

Carbohydrate digestion

Organ pH Enzyme Substrate Product

Mouth Neutral Amylase Starch Maltose

Duodenum Alkaline Amylase Starch Maltose

Ileum Alkaline Maltase Maltose Glucose

In the mouth and duodenum, the enzyme amylase breaks down starch into maltose. In the ileum, maltase then
breaks down maltose to glucose.

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Fat digestion

Organ pH Enzyme Substrate Product

Duodenum Alkaline Lipase Fatty droplets Fatty acids and

glycerol

Ileum Alkaline Lipase Fatty droplets Fatty acids and

glycerol

In the duodenum, fats are firstly emulsified into fatty droplets. The enzyme lipase then breaks down the fatty
droplets into fatty acids and glycerol in both the duodenum and ileum.

Protein digestion

Organ pH Enzyme Substrate Product

Stomach Pepsin Protein Polypeptides

Duodenum Trypsin Polypeptides Peptides

Ileum Peptidase Peptides Amino acids

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Absorption of nutrients in villus

Specialization of villus for absorption

Diagram of a villus of the ileum

Assimilation of end products of digestion:

Nutrient End product Assimilation

Carbohydrates Glucose  Transported to cells and broken down to release energy during
respiration.
 Transported to the liver and converted to glycogen and stored.
Fats Fatty acids and
glycerol

Proteins Amino acids

Table showing the fate of end products of digestion

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Digestion

Factors affecting enzyme activity

 pH
 temperature
 poisons

Graph showing the effect of temperature on enzyme activity.

Graph showing the effect of pH on salivary amylase

All enzymes work best at a certain pH. Any change in the optimum pH of an enzyme will cause it to change its
shape (become denatured) and work less efficiently.

Changes in pH can change the shape of an enzyme so that they may not bind with the substrate to form
products. In general, enzymes have an optimum pH.
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Respiration

Respiration is the release of energy from food.

Types of respiration:

1. Aerobic respiration – is the release of energy from food with the use of oxygen.

Equation for aerobic respiration

2. Anaerobic respiration – is the release of energy from food without the use of oxygen.

Equation for anaerobic respiration in humans

Importance of anaerobic respiration

Anaerobic respiration provides the body with additional energy when doing vigorous activities such as
running, swimming etc. However, this results in the production of lactic acid that causes muscle fatigue. Thus,
the body would have to rest and take in oxygen to breakdown lactic acid and thus overcome muscle fatigue. The
oxygen that the body uses to breakdown lactic acid instead of using it for aerobic respiration is known as
oxygen debt.

Equation for Anaerobic respiration in yeast and plants

Applications of anaerobic respiration

 Yeast are widely used in industries to make alcoholic beverages e.g. wine, beer, vodka
 Organic matter can be placed in bio-digesters where it will be broken down by anaerobic micro-organisms
to form bio-gas such as methane. Methane can be used for cooking.

Difference between aerobic and anaerobic respiration

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Respiration

Cellular respiration

Cellular respiration is the release of energy from food from within the mitochondria.

Cells contain a substance called ADP (adenosine diphosphate) which has two phosphate groups. The energy
released from respiration is used to add another phosphate group to ADP to make ATP. Therefore, the purpose
of respiration is to produce ATP (stored chemical energy) which can later be broken down during various
metabolic activities to release energy.

It is highly advantageous to have ATP since the energy released from food would not be wasted and entirely
loss but stored instead.

ATP

ATP synthase ATPase

+P (Addition of phosphate group) -P (Loss of phosphate group)

Energy is stored Energy is released

ADP

Diagram showing Cellular respiration in mitochondria

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Diagram of Respiratory system

Gaseous exchange in the alveoli

Label the parts of the alveolus P, Q, R and S and the gases Characteristics of gaseous exchange surfaces
A and B.

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Respiration

Gaseous exchange surfaces of organisms

Organisms Gaseous exchange surface

Human Alveoli

Fish

Plants

Cell / unicellular organism

Table showing the gaseous exchange surfaces of organisms

Breathing

Diagram showing the mechanism of breathing

Features Inhalation Exhalation

Ribcage

Intercostal muscles

Diaphragm

Volume Increases Decreases

Pressure Decreases Increases

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Respiration

Components of cigarette smoke and effects

 Nicotine – causes addiction. Causes the lumen (passage way for blood) in arteries to decrease which leads
to a build-up of fats (atherosclerosis). Increases heart rate and nerve impulse transmission (person becomes
more active/alert).

Normal artery Effect of nicotine on artery

 Tar – coats the bronchi and bronchioles leading to inflammation (bronchitis). Bronchitis causes the
passage way for air to decrease making it hard to breathe. Causes cancer: lung cancer, throat cancer, mouth
cancer etc.
 Carbon monoxide – combines with haemoglobin in red blood cells to form carboxyhaemoglobin which
reduces the amount of oxygen that is transported by red blood cells.

Respiratory diseases caused by cigarette smoking

 Bronchitis – inflammation of respiratory tract. This results in constriction of the bronchi and bronchioles.
 Emphysema – destruction of elastic fibres in alveoli leading to loss of function of alveoli.
 Lung cancer – cancer is the uncontrollable division of cells. Cancer may lead to the growth of a large mass
of cancerous cells called a tumor.

Evaluation

1. Which physiological disease(s) is caused by nicotine? Give a reason(s) for your answer. (4 marks)

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Circulation

Types of circulation

1. Pulmonary circulation is the movement of blood from the heart to the lungs and then back to the heart via
the pulmonary blood vessels.

2. Systemic circulation is the movement of blood from the heart to the rest of the body and then back to the
heart.

NB: In reality, both types of circulation occur simultaneously.

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Circulation
Blood Flow through the Heart in 2 MINUTES
Structure and function of the heart
https://www.youtube.com/watch?v=jBt5jZSWhMI

Diagram of heart

Structure Function

Right atrium

Right ventricle

Pulmonary artery

Pulmonary vein

Left atrium

Left ventricle

Aorta

Vena Cava

Valves

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Initiation of heartbeat

The pacemaker is a specialized tissue within the Right atrium that initiates the heartbeat. It receives nerve
impulses from the medulla of the brain and generates an electric signal to cause the cardiac muscles to contract
and thus, it initiates the heartbeat.

Evaluation: The circulatory system

1. Name the chamber of the heart that pumps blood:

(a) To the lungs ______________________________

(b) To the right ventricle _______________________________

(c) To the aorta _______________________________

2. Name the blood vessel which transports blood:

(a) To the lungs _____________________

(b) From the lungs and back to the heart ____________________

(c) To the rest of the body _____________________

(d) From the rest of the body and back to the heart ____________________

(e) To the kidneys _______________________

(f) To the liver _________________________

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(ii) Explain how arterial pressure is affected if structured labelled D is defective (2 marks).
____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

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Circulation

Blood vessels

Features Veins Arteries Capillaries

Size of lumen

Thickness of walls

Muscle and elastic

fibres
Presence of valves

Function

Table showing the differences between the various blood vessels

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Diagram showing blood vessels of circulatory system

Evaluation: Circulatory system and Blood vessels

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Circulation

Components of blood

(i) Red blood cells – transport oxygen. Red blood cells are capable of transporting oxygen because they
contain an iron compound called haemoglobin.

Diagram of various components of blood

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Components of blood

(ii) White blood cells – the function of white blood cells is to destroy foreign invaders (pathogens) such as
bacteria, viruses, fungi etc. There are two main types of white blood cells:
 Lymphocyte – produces antibodies that destroy micro-organisms and anti-toxins that destroy toxins.
 Phagocyte – engulfs and destroys micro-organisms.

Phagocytosis

Diagram showing phagocytosis

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Components of blood

How do White blood cells detect foreign invaders /harmful micro-organisms?

All cells are made up of protein molecules called antigens. Cells that have different antigens from our body
cells are detected as foreign invaders and destroyed by WBC.

(iii) Platelets - are cells that aid in blood clotting.

Blood clotting

Damaged blood vessels release a protein called thromboplastin which converts the enzyme prothrombin into
thrombin. Thrombin then acts on a protein called Fibrinogen and converts it into Fibrin which form a network
which traps platelets and RBC to form the blood clot (scab).

Importance of blood clotting:

(iv) Plasma – liquid portion of blood that transports water, mineral salts, carbon dioxide (hydrogen carbonate),
urea, hormones etc.
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Circulation

Cardiovascular disorders

Diagram showing a normal artery vs. an artery with atherosclerosis

(i) Atherosclerosis – build-up of fats in the arteries.

 Causes

___________________________________________________________________________________

 Effects

___________________________________________________________________________________

___________________________________________________________________________________

___________________________________________________________________________________

 Treatment

___________________________________________________________________________________

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Effect of exercise on circulatory system

During vigorous exercise, the heart rate increases in order to pump more blood at a faster rate to the lungs to
collect oxygen and transport to muscle cells to respire and obtain energy and break down lactic acid to relieve
muscle fatigue. CO2 is also pumped to the lungs so that it can be removed from the blood via gaseous
exchange.

Exercising at high altitude

Generally, the higher the altitude, the less oxygen is available in the atmosphere. If someone exercises at high
altitude, the body would adapt to this change in surroundings by producing more red blood cells to collect more
oxygen from the atmosphere.

Therefore, when they return to a normal altitude, they would have more red blood cells to supply their muscles
with oxygen for aerobic respiration to supply more energy during vigorous activities.

Questions on Circulation

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5. Which of the following components of blood would engulf viruses?

_________________________________________________________________________________________

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Transport in plants

Materials that need to be transported by plants and animals: carbon dioxide, oxygen, minerals, glucose,
amino acids, water, hormones etc.

Importance of a transport system

Organisms need a transport system to move substances around their body so that they can:

 carry out metabolic activities e,g. respiration

 make organic molecules
 eliminate harmful products.

Surface area to volume ratio

Below we have two organism A and B which are made up of cells. Which one has the larger surface area to
volume ratio?

Features A B

Surface area

(L x B x number of sides)

Volume
(L x B x H)

Surface area/Volume ratio

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Transport in plants

Benefits of high surface area to volume ratio

 Faster rate of diffusion of gases and nutrients in and out of their cells

 Faster rate of osmosis in and out of cells

 Require a less complex transport system to move substances around their body

Dicot root

Pathway of water from soil into xylem vessel

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Structure and function of xylem vessel

Diagram of xylem

Specialization of xylem for water transport

 Hollow tube that is made up of dead cells (no cytoplasm which crates more space) which creates a large
surface area for water transport
 Has pits that distribute water to nearby cells
 Cell wall of xylem is made of cellulose and lignin which provides support and makes it sturdy
 No end walls in cell walls which creates more space for water transport
 Xylem has a small diameter which promotes capillarity

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Transport in plants
Youtube: Class 7 | Transpiration in Plants | Science | NCERT | CBSE Board | Home Revise
Transpiration
https://www.youtube.com/watch?v=LFyUDUi5WQI

Transpiration is the loss of water through the stomata of the leaf. Transpiration stream is the pathway of water
from the root to the leaf.

Diagram showing transpiration stream

Role of transpiration:

 Cools down the plant - as water exits the stomata and moves onto the leaf, the water absorbs heat from the
surface of the leaf in order to evaporate and thus cools down the plant

 Allows cells of leaf to receive water for photosynthesis

 Allows cells to receive mineral salts

 As stomata open to release water, CO2 is also absorbed for photosynthesis

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Youtube: Factors Affecting Transpiration | GCSE Biology
Movement of water up the xylem
https://www.youtube.com/watch?v=SGxI-n5MCx4

Water moves into and up the xylem by three main ways:

 Osmosis – water moves from high concentration from the soil and then to a low concentration into the root
hairs and eventually into the xylem via osmosis.

 Transpiration pull - the suction force which pulls water from the root to leaves due to the opening of the
stomata. Opening of the stomata lowers the pressure in the leaves which causes water to be pulled up the
xylem.

 Diffusion – when there is a high concentration of water in the leaf and a low concentration of water in the
atmosphere, a concentration gradient is created and thus water exits the leaf via diffusion.

Factors that affect the rate of transpiration

 Light intensity – an increase in light intensity causes the stomata to open to absorb CO2 for photosynthesis
and at the same time water exits by transpiration. Thus: Light intensity Transpiration

Diagram showing effect of light intensity on rate of transpiration

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Factors that affect the rate of transpiration

 Temperature – an increase in temperature increases the kinetic energy of water molecules and thus it to
move faster up the xylem and out through the stomata. An increase in temperature also increases the rate of
evaporation of water from the surface of leaves leading to more water loss leaves.
Thus: Temperature Transpiration

 Wind velocity – the wind blows away the water vapour from the surface of leaves and thus creates a low
concentration gradient in the air around the leaf. Therefore, water in the leaf (high concentration) diffuses
out of the leaf and into the atmosphere (low concentration). Thus: Wind velocity Transpiration

 Humidity – when there is a low humidity in the atmosphere (low concentration of water molecules), a
concentration gradient is created. Thus, water from the leaf (high concentration) moves to the atmosphere
(low concentration). Thus: Humidity Transpiration

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1. Construct a graph to display the information above. (6 marks)

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Transport in plants

Phloem vessel

The phloem vessel transports food (sucrose).

Diagram of phloem

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Translocation

Translocation refers to the movement of food (sucrose) from the source to the sink.

 Source – refers to the parts of the plant that photosynthesize e.g.

 Sink – refer to the parts of the plant that store the sucrose e.g.

How a plant stores food - the excess glucose that a plant makes during photosynthesis is converted to sucrose
and then transported from the leaf to various storage organs such as the stem root, leaves, fruit etc. and to be
stored as sucrose OR converted to starch and stored.

Importance of storage:

 Storage as a means of overcoming the need for continuous food intake and production
 Providing for periods of scarcity during harsh conditions such as drought
 Providing a readily available supply of nutrients for reproduction, growth etc.
Storage product Storage site in plants Storage site in animals

Starch Leaf, stem, root, seed etc. -

Sucrose Stored in fruits -

Glycogen - Stored within glycogen granule within cells especially liver

Fats and oils Seeds, fruits Liver, fat deposits around body

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