Biology Unit Two Revision Notes (higher)

Tell me if you think I missed anything!

HideShow resource information
  • Created by: Angharad
  • Created on: 16-05-10 17:40
Preview of Biology Unit Two Revision Notes (higher)

First 352 words of the document:

Unit Two
Most human cells like most other animal cells have:
Mitochondria: where most energy is released in respiration
Ribosomes: where protein synthesis occurs
Nucleus: controls cell's activities, contains genetic material
Cytoplasm: where most chemical reactions take place,
controlled by enzymes
Cell membrane: controls the passage of substances in and out of the cell
Plant cells often have:
Cell wall: strengthens the cell, made of cellulose
Chloroplasts: contains chlorophyll, absorb light energy to
make food
Permanent vacuole: filled with cell sap, helps keep the
cell turgid
Cells may be specialised to carry out a particular function:
Sperm cells:
Long tail: swim better
Middle section: full of mitochondria to release
lots of energy
Acrosome: enzyme in head dissolves outer layer
of egg
Large nucleus: pass on genetic information
Red blood cells:
Biconcave: increased surface area: volume ratio, more efficient
absorption of oxygen
Thin outer membrane: lets oxygen diffuse easily
No nucleus: more space for haemoglobin, which carries oxygen
To get in or out of cells, dissolved substances have to cross the cell membranes. This can be
done by diffusion and osmosis.
Diffusion: the passive process of particles moving from an area of high concentration to an
area of low concentration.
The greater the difference in concentration, the faster the rate of diffusion.
Oxygen required for respiration passes through cell membranes by diffusion.
Osmosis: the diffusion of water from a dilute to a more concentrated solution through a
partially permeable membrane that allows the passage of water molecules.
Differences in the concentrations of the solutions inside and outside a cell cause
water to move into or out of the cell by osmosis.
Plants gain water by osmosis through their roots. Water moves into plant cells
making them turgid so the cell can hold out its leaves and hold its stem upright as
cell contents is pushed against the cell wall.

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

If plant cells lose a lot of water from their stomata or are placed in a concentrated
solution such as salt water, cells become plasmolysed as cell membrane pulls away
from cell wall, leading to wilting.
Plants can make their own food by photosynthesis.
Things required for photosynthesis:
1. Light: from the Sun
2. Chlorophyll: in leaves
3. Carbon Dioxide: enters through stomata
4.…read more

Page 3

Preview of page 3

Here's a taster:

Used in respiration: releases energy
Making cell walls: glucose into cellulose
Making proteins: glucose combined with nitrates to make amino acids, then made
into protein
Stored as insoluble starch in cells
Plants need to take in a number of elements to stay alive.…read more

Page 4

Preview of page 4

Here's a taster:

Animals unable to behave naturally
Free-range farming
Can charge more for produce
Animals live more naturally
More land needed
Lower yield
A balance must be reached between a farmer's needs and the animal's welfare.
The Carbon Cycle and decay
Living things remove materials from the environment for growth and other
processes. These materials are returned to the environment either in waste materials
or when living things die and decay.
Materials decay because they are broken down, (digested), by micro-organisms.…read more

Page 5

Preview of page 5

Here's a taster:

Once the microorganisms and detritus feeders have broken down the waste
products and dead bodies of organisms in ecosystems and cycled the materials as
plant nutrients, all the energy originally captured by plants has been transferred.
Enzymes are biological catalysts, (they increase the rate of a reaction).
Enzymes are protein molecules made up of long
chains of amino acids. These long chains are
folded to produce a special shape which enables
the substrate to fit into the enzyme.…read more

Page 6

Preview of page 6

Here's a taster:

Small intestine Lipase Lipids (fats and Fatty acids Small intestine
oils) and glycerol
The stomach also produces hydrochloric acid, around pH2, (strong enough to
kill most microbes). The enzymes in the stomach work most effectively in
these acid conditions. Also produces protease, (inactive until secreted:
prevents it from digesting stomach wall).
The liver produces bile which is stored in the gall bladder
before being released into the small intestine. Bile neutralises the acid
that was added to food in the stomach.…read more

Page 7

Preview of page 7

Here's a taster:

Waste products which have to be removed from the body include:
Carbon dioxide produced by respiration: leaves via the lungs when we exhale
Urea produced by the liver breaking down excess amino acids: removed from the
blood by the kidneys, (by ultra filtration), into the urine, stored in the bladder.
Internal conditions which are controlled include:
1. Water and ion content of the body
If the water/ ion content is wrong, too much water may move into/ out of the cells,
damaging them.…read more

Page 8

Preview of page 8

Here's a taster:

If the core body temperature is too high:
Blood vessels supplying the skin capillaries dilate so that more blood flows through
the capillaries and more heat is lost.
Sweat glands release more sweat which cools the body as it evaporates.
If the core body temperature is too low:
Blood vessels supplying the skin capillaries constrict to reduce the flow of blood
through the capillaries, less heat is lost.
Muscles `shiver,' the contraction needs respiration which releases some heat energy.…read more

Page 9

Preview of page 9

Here's a taster:

In body cells the chromosomes are normally found in pairs. Body cells divide by mitosis to
produce identical daughter cells during growth and repair.
Cells in reproductive organs, testes and ovaries in humans, divide to form gametes.
The type of cell division is called meiosis.…read more

Page 10

Preview of page 10

Here's a taster:

Homozygous recessive/ dominant: has two alleles that are the same, (two
recessive or two dominant).
Heterozygous: has two different alleles, one recessive, one dominant.
Phenotype: the physical appearance/ characteristic produced by a genotype.
Each gene codes for a particular combination of amino acids which make a specific protein.
Each person, (except identical twins), has unique DNA. This can be used to identify individuals
in a process known as DNA fingerprinting, used to solve crimes and paternity cases.…read more


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »