The document discusses various biological processes involved in respiration, nutrient absorption, and gas exchange in humans and plants, highlighting the roles of lungs, small intestines, and root systems. It explains how blood circulation facilitates the transport of oxygen, nutrients, and waste, along with details on anaerobic respiration and fermentation in microorganisms. Additionally, it covers kidney function and treatments for kidney failure, including dialysis and transplantation, along with the use of fermentation for producing biogas and ethanol-based fuels.

1. Unit Biology 3
Lungs, absorbing food and plants
Dissolved substances move by diffusion.
Substances are sometimes absorbed against a concentration gradient. This requires the
use of more energy from respiration. The process is called active transport. It enables
cells to absorb ions from very dilute solutions.
In humans:
o the surface area of the lungs is increased by the alveoli
o surface area of small intestine by villi
The lungs are separated from the lower part of the body (abdomen) by the diaphragm.
The breathing system allows oxygen from the air to diffuse into the bloodstream and
carbon dioxide to diffuse out of the bloodstream into the air.
Adaptations for gas exchange:
o Lungs have millions of tiny alveoli giving them large surface area
o Alveoli have a moist thin layer of water
o Rich supply of bloo vessels
o Walls of alveoli = one cell thick, diffusion takes place easily, + efficiently
Small intestine adapted to absorb + digest food:
o 3 metres long, therefore long length for absorption + diffusion of substances to
take place
o Finger like projections -the villi- provide a large surface area with
o an extensive network of capillaries to absorb the products of digestion by
diffusion and active transport. (transports absorbed glucose + amino acids into
blood system ) (transports fats into lymphatic system)
o Each villus has a branch of the lymphatic system for transporting fats – makes it
a lot easier.
o Micro villi found on villi – expand SA further. Found in the ileum (end of the
small intestine)
In plants:
o carbon dioxide enters leaf cells by diffusion
o most of the water and mineral ions are absorbed by root hair cells by active
transport
o Surface area of roots is increased by root hairs
o surface area of leaves by the flattened shape and internal air spaces.
Plants have stomata to obtain carbon dioxide from the atmosphere.
Plants lose water vapour from the surface of their leaves.
This loss of water vapour is called transpiration.
Factors affecting transpiration:
o rapid in hot
o dry
o windy conditions

2. Most of the transpiration is through stomata. The size of stomata is controlled by guard
cells which surround them. If plants lose water faster than it is replaced by the roots, the
stomata can close to prevent wilting.
Transporting blood
Substances are transported around the body by the circulation system:
o Heart
o blood vessels
o blood
. Blood flows from the heart to the organs through arteries and returns through veins.
In the organs, blood flows through capillaries.
Substances needed by cells in the body tissues pass out of the blood
Waste substances produced by the cells pass into the blood through the walls of the
capillaries.
There are two separate circulation systems (double circulation), one to the lungs and one
to all the other organs of the body.
Blood plasma transports:
o carbon dioxide from the organs to the lungs
o soluble products of digestion from the small intestine to other organs
o urea from the liver to the kidneys.
o RBC
o Platelets
o WBC
Red blood cells:
o transport oxygen from the lungs to the organs.
o are packed with a red pigment called haemoglobin
Haemoglobin combines with oxygen to form oxy-haemoglobin.
When blood is pumped to tissues + organs, splits into oxygen + haemoglobin and
oxygen diffuses out of the capillaries.
Exercise and respiration
The energy that is released during respiration is used to enable muscles to contract.
During exercise a number of changes take place:
o Heart rate increases
o Rate and depth of breathing increases
o Arteries supplying the muscles dilate.
o Glycogen stores in the muscle are used during exercise.
These changes increase the blood flow to the muscles and so increase the supply of
sugar and oxygen and increase the rate of removal of carbon dioxide.
Anaerobic respiration is the incomplete breakdown of glucose - produces lactic acid

3. Much less energy is released than during aerobic respiration.
Anaerobic respiration results in an oxygen debt that has to be repaid in order to oxidise
lactic acid to carbon dioxide and water.
Microbiology
bacteria are used in yoghurt and cheese manufacture
Yeast is used in making bread and alcoholic drinks.
Yeast is a single-celled organism.
Yeast can respire without oxygen (anaerobic respiration), producing carbon dioxide and
ethanol (alcohol).
This is called fermentation.
Aerobic respiration provides more energy and is necessary for the yeast to grow and
reproduce.
In brewing beer and wine-making, carbohydrates are used as an energy source for yeast
to respire.
For making beer:
o the starch in barley grains is broken down into a sugary solution by enzymes in a
process called malting to form a sugar called maltose
o the sugary solution is extracted then fermented
o Hops are then added to give the beer flavour.
In wine-making:
o Yeast uses natural sugars in grapes as its energy source.
In the production of yoghurt:
o a starter of bacteria is added to warm milk
o the bacteria ferment the milk sugar (lactose) producing lactic acid
o the lactic acid causes the milk to clot and solidify into yoghurt.
Industrial fermenters usually have:
o an air supply – to provide oxygen for respiration of the microorganisms
o a stirrer to keep the microorganisms in suspension and maintain an even
temperature
o a water-cooled jacket to remove heat produced by the respiring microorganisms
o instruments to monitor factors such as pH and temperature.
The antibiotic, penicillin, is made in a fermenter. The medium contains sugar and other
nutrients
The Penicillium only starts to make penicillin after using up most of the nutrients for
growth.
The fungus Fusarium is used to make mycoprotein, a protein-rich food suitable for
vegetarians.
The fungus is grown on starch in aerobic conditions and the biomass is harvested and
purified.

4. Biogas
Fuels can be made from natural products by fermentation.
Biogas, mainly methane, can be produced by anaerobic fermentation of a wide range of plant
products or waste material containing carbohydrates.
On a large scale, waste from sugar factories or sewage works can be used
On a small scale, biogas generators can be used to supply the energy needs of individual
families or farms
Many different microorganisms are involved in the breakdown of materials in biogas
production
Ethanol-based fuels can be produced by the anaerobic fermentation of sugar cane juices
and from glucose derived from maize starch by the action of carbohydrase. The ethanol
is distilled from the products of the fermentation and can be used in motor vehicle fuels.
People whose kidneys do not function properly die because toxic substances
accumulate in their blood. Their lives can be saved by using dialysis machines or
having a healthy kidney transplanted.
Candidates should use
their skills, knowledge and
understanding of how science
works:
to evaluate the advantages and disadvantages of treating kidney
failure by dialysis or kidney transplant.
Their skills, knowledge and
understanding of how science
works should be set in these
substantive contexts:
A healthy kidney produces urine by:
first filtering the blood
reabsorbing all the sugar
reabsorbing the dissolved ions needed by the body
reabsorbing as much water as the body needs
releasing urea, excess ions and water as urine.
HT 
Sugar and dissolved ions may be actively absorbed against a
concentration gradient.
People who suffer from kidney failure may be treated either by
using a kidney dialysis machine or by having a healthy kidney
transplanted.
In a dialysis machine a person’s blood flows between partially
permeable membranes. The dialysis fluid contains the same
concentration of useful substances as the blood. This ensures that
glucose and useful mineral ions are not lost. Urea passes out from
the blood into dialysis fluid. Treatment by dialysis restores the
concentrations of dissolved substances in the blood to normal
levels and has to be carried out at regular intervals.
Biology - General Certificate of Secondary Education, 2012 examination

5. 52 hij
A kidney transplant enables a diseased kidney to be replaced with
a healthy one from a donor. However, the donor kidney may be
rejected by the immune system unless precautions are taken.
To prevent rejection of the transplanted kidney:
a donor kidney with a ‘tissue-type’ similar to that of the
recipient is used
the recipient is treated with drugs that suppress the immune
system.