Download YEAR 10 IGCSE BIOLOGY REVISION GUIDE DBGS DIGESTION

YEAR 10
IGCSE BIOLOGY
REVISION GUIDE
DBGS
Prepared by William Green 2011
DIGESTION AND NUTRITION
Digestion is presented as a means of transforming complex food substances into smaller molecules prior to absorption
into the body. The functions of the human digestive systems are examined, as well as the role of enzymes as catalysts.
Digestion is the breaking down of large molecules of food into smaller ones, eventually going into the blood.
1. Mechanical Digestion
2. Chemical Digestion
Enzymes
 Salivary glands make amylase
 Glands in stomach (Gastric Glands) make Pepsin (Protease)
 Pancreas make amylase, lipase, trypsin (Protease)
Enzyme Functions
 Amylase breaks down starch into maltose
 Protease (pepsin, trypsin) breaks down protein into polypeptides
 Lipase breaks down fat into glycerol and free fatty acids

Test for starch: Iodine turns from brown to black
Test for glucose: heat substance in water bath with Benedict’s solution, will turn orange if glucose is present
How absorption is increased in small intestine
 Villi: folds, increase surface area
 Each villus: has many blood capillaries
Factors which affect enzyme activity
 pH, there is an optimum pH, above or below this results in denaturation
 Temperature, there is an optimum temperature.
o In body 37o C is optimum
o Low temperature slows down enzymes
o High temperature permanently denatures enzymes
What is an enzyme
 A protein which acts as a catalyst, which speeds up the rate of reaction.
When enzymes are used
 Washing up powder. Protease breaks down protein stains.
Function of large intestine
 absorb - water, vitamins, and minerals
 colon produces vitamin K
This section provides the opportunity for investigating how the human breathing system allows the exchange of fasces
between alveoli and the blood capillaries. The effects of cigarette smoke on health are considered.
Prepared by William Green 2011
GAS EXCHANGE
Structure of the Breathing System
Alveoli and Gaseous Exchange






How we
clean the
we breath
There are millions of alveoli, therefore large surface
area
surface lining is moist, so gasses can dissolve before
diffusing
Thin membrane
pulmonary artery brings deoxygenated blood
pulmonary vein brings oxygenated blood
diffusion of oxygen and carbon dioxide into and out of
the blood
air
Prepared by William Green 2011


Lining the nose and lungs are goblet cells, which produce mucus
dirt and germs get caught in the mucus and is flicked up back to the mouth by cilia.
Smoking and Lung Disease
 CO - reduces the oxygen carrying capacity of the blood
 Nicotine - is addictive, relaxes muscles, raises blood pressure, and increases fatty substances in the blood
 Smoking causes
 smokers cough - mucus gets caught in bronchioles cilia, and are too clogged up to flick mucus back up
 Bronchitis - bursts alveoli walls (emphysema) therefore a reduced area for oxygen and carbon dioxide to
diffuse.
 Cancer - carcinogens in tobacco cause cells to divide more than they should. This causes a tumour.
 Heart Disease - tendencies for blood to clot will increase, due to increased fat.
 Tar - clogs up cilia
Composition of air breathed in and out
Inhaled
Exhaled
Oxygen
21%
16%
CO2
0.04%
4%
Nitrogen
79%
79%
Water Vapour
Little
Lots
Breathing In
 Intercostal muscles contract
 diaphragm moves down (contracts)
 Ribs move up and out
 Thorax volume increases, pressure decreases
 air drawn into lungs
Breathing Out
 Intercostal muscles relax
 diaphragm relaxes
 Ribs move down and in
 Thorax volume decreases, pressure increases
 air forced out of lungs
TRANSPORT SYSTEM
This section allows transport systems to be examined. The need for transport systems in large organisms is considered,
together with the ways in which the major transport systems of plants and mammals function.
Red Blood Cells - Erythrocytes
 Carry oxygen around the body (haemoglobin)
 No nucleus (More oxygen carrying possible)
 Biconcave - maximum surface area
 Haemoglobin combines with oxygen - oxyhaemoglobin
 lack of haemoglobin - anaemic
 5 million Red Blood Cells per mm3
White Blood Cells - Leukocytes
 Irregular shape
 7000 per mm3
 Phagocytes (engulf the bacteria)
o bacteria into vacuole
o enzymes destroy it
Prepared by William Green 2011

Lymphocytes
o Produces antibodies which recognise antigen on bacteria membrane
o disable bacteria
o finally ingested by phagocytes
o immunity
Platelets
 fragments of cells
 250000 per mm3
 they clump together to clot blood
 make chemical that converts fibrinogen into fibrin - strands across wound.
Plasma



contains fibrinogen
contains serum, water, salts, gasses, hormones, glucose and wastes
It is made up of 90% water.
Substances Transported by the Blood
Substance
From
To
Oxygen
Lungs
Body Cells
Carbon Dioxide
Body Cells
Lungs
Urea
Liver
Kidney
Food (Glucose)
Intestine
Body Cells
Hormones
Glands
Target Organs
Heat
Muscles/Liver
Whole Body
Transport Systems - Veins, Arteries, Capillaries
 Arteries carry oxygenated blood away from the heart around the body
 Veins carry deoxygenated blood from the body to the heart and then to the lungs
 Capillaries link arteries to veins. They are the site of diffusion with tissue
 Veins have valves to prevent backflow of blood
 Veins have a thin wall
 Arteries have thick walls, this allows from stretching (pulse)
 Arteries have a narrow lumen, allowing for high pressure
 Coronary arteries are around the heart
 The heart has double circulation, meaning blood goes through the heart twice, once oxygenated, and once
deoxygenated.
 Cholesterol can cause blocking of the coronary arteries
 It can also cause blood pressure to increase.
Prepared by William Green 2011
RESPIRATION
Respiration – takes place in plants and animals
Aerobic Respiration
 with oxygen
 Glucose + oxygen -> Carbon dioxide + Water + Energy
 C6H12O6 + H2O -> CO2 + H20 + Energy
Anaerobic Respiration
 without oxygen
 Glucose -> Energy + Lactic Acid (Instead of CO2)
 Lactic Acid builds up in the muscles and makes them ache. Muscle cramps
 To get rid of lactic acid, aerobic respiration occurs
 Lactic acid + O2 -> CO2 + H20 + Energy
 Amount of oxygen required in the above is called oxygen debt
Differences Between Aerobic and Anaerobic Respiration
Aerobic
Anaerobic
Required Oxygen
No oxygen
No lactic acid
Lactic Acid produced
Large amount of energy
Less energy released
Water and Carbon Dioxide produced
Lactic Acid and energy produced. (No CO2 and H20)
Uses of Energy produced
 making muscles work
 growth and repair of cells
 maintaining body temperature
 transport of substances in the blood
 never impulse
 plants use energy for photosynthesis
Prepared by William Green 2011
CELLS AND LIVING ORGANISMS
This section looks at the cell as the basic unit from which most living organisms are constructed. The pats of a cell are
identified and their functions considered. Differences between plant and animal cells performing different functions
within a plant or animal are discussed. The particular role of the cell membrane in the uptake or loss of water is
examined.
All living organisms are made up of cells
Know the diagram of plant and animal cell, as well as labelling
Differences between plant and animal cells:
Plant
Animal
Cell Wall
no cell wall
Permanent vacuole
temp. vacuole
chloroplast
no chloroplast
starch grains
glycogen granules
regular shape
irregular shape
Definitions
Nucleus
 controls chemical reactions
 contains information to make living organism
 tells cell what to do
Cytoplasm
 where chemical reactions take place
Cell Membrane
 controls what comes in and goes out of cell
Cell Wall
 made of cellulose
 gives cell strength and support
Vacuole
 contains salt and sugar solution, called cell sap
 supports cell
Chloroplast
 contains chlorophyll
 for photosynthesis
Mitochondria
 release energy by cellular respiration
A group of specialised cells working together are called tissue
Prepared by William Green 2011
Osmosis and Diffusion
Diffusion is the movement of molecules from an area of high concentration to an area of low concentration., until
equilibrium is reached.
 Larger Molecules - slower rate of diffusion
Osmosis is the movement of water molecules from an area of high concentration (weak solution) to an area of low
concentration (strong solution), though a partially permeable membrane, until equilibrium is reached.
 when plant cell vacuoles swell up, cells become turgid
 when lacking water, the plant wilts, and the cells become flacid
 when lots of water leaves, cytoplasm comes away from cell wall, this is called plasmolysis
HOMEOSTASIS
Homeostasis is defined as the maintenance of constant internal conditions within organisms. The principle can be
developed in a wide range of contexts, including the maintenance of balanced water levels in the blood, the regulation
of body temperature in mammals, the regulation of blood glucose levels and the removal of excretory products, such
as urea.
Osmoregulation: the regulation of water levels by the kidney
 Low water level in blood
o water is reabsorbed from the kidney nephron into the blood
 concentrated urine produced
 high water levels in the blood
o less water is reabsorbed from filtrate in the kidney nephron
 dilute urine produced
Excretion: is the removal of waste products of metabolic reactions made inside the
body cells
The kidney
Purpose
1. removal of nitrogenous waste (urea)
2. production of urine
3. osmoregulation
Removal of Urea
 urea is made in liver
 amino acids -> ammonia -> urea -> blood transports it to the kidney
Production of Urine
Kidney has filtration units called nephrons (they clean the blood)
Types
1. Ultrafiltration: small molecules are filtered through the nephrons, large
molecules, such as red blood cells and proteins are not filtered.
2. Selective Reabsorption: useful molecules are returned to the blood. The rest is
sent to the bladder as urine.
Humans are endothermic, warm blooded. Have body temperature of 36.7oC.
Prepared by William Green 2011
Homeostasis: the maintenance if internal conditions within an organism
1. balance of water levels (osmoregulation)
2. regulation of body temperature
3. regulation of blood glucose level
4. removal of excretory products
Regulation of body temperature
 Sweating - sweat glands - lets out a solution of urea, salt and water
 Vasodilation & Vasoconstriction
o Hot Weather - Vasodilation
 capillaries close the skin dilate
 increased blood flow through skin
 heat loss by radiation
 skin fells warmer and looks redder
o Cold Weather - Vasoconstriction
 capillaries close to skin constrict
 reduced blood supply to the skin
 less heat lost through skin
 skin feels cold and looks pale
Regulation of Glucose levels
 Carbohydrate (stimulus): Pancreas (receptor) -> stimulated and secretes hormone insulin -> insulin decreases
glucose levels to normal
 Insulin causes body cells to absorb more glucose and change it into glycogen
o Diabetes: when pancreas doesn’t create insulin. Diabetics take insulin shots.
 It is not taken orally because it is a protein and would be digested by protease
All organisms respond to changes in their environment and this section explores some of the ways in which they do
this. The human eye is studied as an example of a receptor organ.
COORDINATION
Stimuli: Changes in external or internal environment which cause a response
Receptor: Cells in the body which detect stimuli
Effector: Part of the body which responds to stimuli
Central Nervous System
1. Brain
2. Spinal Chord
Nerves: a bundle of nerve cells. A nerve cell is called a neurone.
1. Sensory Neurone: Carries impulses from the receptor to the central nervous system
2. Motor Neurone: Carries impulses from teh central nervous system to the effectors
3. Relay neurone: connects the sensory neurone to the motor neurone.
Prepared by William Green 2011
Motor Neurone


Myelin Sheath: Is fatty and insulates electricity inside the axon.
Dendrites: Receive nerve impulses from sensory cells.
Reflex Action, Involuntary/Voluntary
 Reflex arc is the path taken by an impulse in a reflect arc
 Stimulus->Receptor->Sensory neurone->Relay neurone->Motor Neurone-> Effector->Response
Spinal Chord (Reflex arc only concerned with stimulus from the skin)
 Stimulus (sharp object) -> Sensory neurone (through dorsal route in white matter) -> (synapse in grey matter)
-> relay neurone -> (synapse) -> motor neurone (in white matter) -> muscle effector (move hand)
The Eye
Know the structure of the eye.
How we see
 Light rays from objects are refracted by the cornea and focussed by the lens. This forms an upside down
image on the retina. This upside down image is corrected by our brain so we see the correct way up.
Focussing on Distant objects
1. ciliary muscles relax
2. suspensory ligaments become tight
3. lens get pulled thin and flat. (less convex)
4. It is the first of the above images
Focussing on near Objects
1. ciliary muscles contract
2. suspensory ligaments relax
3. lens becomes fatter and rounder (more convex)
4. second of above images
Prepared by William Green 2011
Rods and Cones: Contain light sensitive pigments which are bleached in light and generate an impulse
Rods
Cones
120 million present
6 million present - mainly on fovea
sensitive to low light concentrations
sensitive to bright light concentrations
black and white image
colour image
fuzzy image
sharp and clear image
PHOTOSYNTHESIS
This section examines the physiology of photosynthesis and how it related to agriculture and food production. The
value of photosynthesis as an oxygen producing process is examined and is related to the maintenance of the
composition of the atmosphere.
Photosynthesis is a chemical reaction in plants to make food. It only occurs in the presence of light.
Word Equation

Carbon Dioxide + Water
glucose + oxygen
Symbol Equation
 CO2 + H20 --> C6H12O6 + O2
Requirements for Photosynthesis
 Light Energy
 CO2
 H20
Rate of Photosynthesis - can be measured by how much O2 is given off.
Limiting Factors - you need all three for photosynthesis to occur
 Light - Light increases, rate of photosynthesis increases up to a certain point
 CO2 - CO2 increases, rate of photosynthesis increases up to a certain point
 Temperature - must not get too hot or too cold
Overcoming Limiting Factors
 Light - artificial light, during night, especially red or blue, grow in unshaded areas
 CO2 - Have a canister of CO2 in greenhouse
 Temperature - find a warmer place. Use a greenhouse
Prepared by William Green 2011
The Leaf
1.
2.
3.
4.
CO2 enters through the stomata
Spongy cells have a space for exchange of gasses
Chloroplasts in palisade cells, on the upper surface of leaf, most light on that part
Xylem - Carries water from roots to leaf. Phloem carries glucose from leaves to rest of the plant.
Is starch produced by photosynthesis?
 Put leaf in boiling water for 15 seconds. This kills it, makes it soft, makes cell walls permeable
 Put leaf in alcohol in test tube. Put the test tube in hot water bath. This decolourises it.
 Remove and wash the leaf
 Put iodine of the leaf
 If starch is present, the leaf turns blue black.
Nitrogen - Nitrogen as nitrates is absorbed from the soil to make protein.
You will also need to know tests for whether a plant needs light, does it need CO2 , and is O2 produced.
The first two can be done with putting them without the variable, and then testing for starch.
TRANSPORT IN PLANTS
Water and minerals are absorbed by the root hairs and then into the xylem
Xylem and Phloem
Xylem transports water from root hairs to leaves
Phloem transports glucose from leaves to the rest of the plant
Transpiration- it is the movement of water from root hairs to leaves where it evaporated and is released through the
stomata
 The evaporation causes suction due to the difference in pressure, and pulls water up through the leaves.
 This continuous cycle is known as a transpiration stream.
Functions of transpiration
 Cools plant
 Brings water and minerals to the plant
Prepared by William Green 2011
Differences between the Xylem and Phloem
Xylem
Phloem
Dead tissue make it up
living tissue
vessels lined with lignin
vessels lined with cellulose
Transports Water
Transports glucose
Environmental Factors Affecting Transpiration
 Light
o opens the stomata, therefore more evaporation
 temperature
o on a hot day evaporation occurs more rapidly
 Air Movement
o Wind removed water vapour around the leaf
 Humidity
o Low humidity, therefore higher concentration of water vapour in leaf the air. (diffusion high)
Potometer - measures water uptake by roots
This section introduces respiration as a process for transferring energy from food (e.g. glucose) to the cells of an
organism. Oxygen is normally required for respiration and carbon dioxide is produced as a waste product.
REPRODUCTION IN PLANTS
No individual organism is immortal; reproduction avoids extinction. Most organisms reproduce sexually, many
asexually as well
Asexual methods of reproduction
- Binary fission, bacteria
- Spores, fungi
- Budding, yeast
- Identical twinning, a single zygote may develop into two babies
- Vegetative propagation, outgrowths of new plantlets
Types of vegetative propagation
- Runners, strawberry
- Rhizomes, raspberry
- Stem tubers, potato
- Bulbs, daffodil
Plants can also be asexually reproduced artificially. This allows for maintaining good varieties of house-plants, and
some crops, rapidly multiply new varieties, selective breeding, maintain seedless crops such as oranges and grapes.
1. Cuttings are lengths of stems or leaves
2. Grafting is the insertion of a shoot or bud from one plant to a related plant
3. Tissue culture is a fast way of producing plants genetically identical. Small amounts of partent plant tissue
are grown on agar into plantlets
Prepared by William Green 2011
A flower is the organ of sexual reproduction in flowering plants
Peduncle: The stalk of a flower.
Receptacle: The part of a flower stalk where the parts of the flower are attached.
Sepal: The outer parts of the flower (often green and leaf-like) that enclose a developing bud.
Petal: The parts of a flower that are often conspicuously coloured.
Stamen: The pollen producing part of a flower, usually with a slender filament supporting the anther.
Anther: The part of the stamen where pollen is produced.
Pistil: The ovule producing part of a flower. The ovary often supports a long style, topped by a stigma. The mature
ovary is a fruit, and the mature ovule is a seed.
Stigma: The part of the pistil where pollen germinates.
Ovary: The enlarged basal portion of the pistil where ovules are produced
There are two main stages in sexual reproduction
1. Pollination: transfer of pollen from stamens to stigmas
2. Fertilization: fusion of male gamete with female gamete inside the ovule. This results from the growth
of pollen tubes from the pollen on the stigmas to the ovules
Pollination of a flower can be either self pollination or cross pollination:
Self pollination is the transfer of pollen from the stamen to any stigma on the same plant.
Cross pollination is the transfer of pollen from the stamen of one plant to the stigma of a different plant
Comparisons of flowers adapted for wind or insect pollination
Position of stamen
Position of stigma
Type of stigma
Size of petals
Colour of petals
Nectaries
Pollen grains
Insect pollinated
Enclosed with flower
Sticky
Large
Brightly coloured
Present as a reward
Larger, sticky grains
Wind pollinated
Exposed
Feathery
Small
Not brightly coloured, usually green
Absent
Smaller, smooth inflated grains
Prepared by William Green 2011
Plant Fertilisation
Fruit and Seed dispersal
Fruits serve two main functions.
1. Protection of the seed
2. Dispersal of the seed
Seeds are designed are dispersed either by wind, water, animal or eaten
PLANTS RESPONSE TO THE ENVIRONMENT
Phototrophic response: growth in response to directional stimulus, light
Top of the plant shoot is the receptor of light for growth
Auxin is a chemical growth regulating substance, which is produced at the tip of shoots when exposed to light.
 Auxin diffuses down the shoot, on the side which is shaded
o it causes cells in zone of cell elongation to grow faster
o therefore one side is long/bigger than the other, so the plant bends towards the light.
Tropisms are the growth movement of a plant toward or away from a stimulus. Usually controlled by hormones
Light
Gravity
Phototropic
Geotropic
Phototropisms uses the hormone auxin at the shoot tips.
Geotropism uses auxin in the root at the root tips
Also go to BBC KS4 Bitesize, www.biology-resources.com/biology-questions.html or
www.biotopics.co.uk/newgcse/intro.html
Prepared by William Green 2011