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Homeostasis
Controlling conditions:
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The conditions need to be kept constant to keep the body working correctly
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The conditions inside the body are called the internal environment
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It’s important to keep conditions constant to the cells can function properly, for example, enzymes
can work in the optimum conditions
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Homoeostasis is the maintenance of a constant internal environment
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It is the regulation of the internal conditions of a cell or organism to maintain optimum conditions
for function in response to internal and external changes

Control system:
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Stimulus - changes in the environment
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Coordination centre - areas they receive and process information, such as the brain, spinal-cord
and pancreas
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Effector - muscles or glands that bring about a response between store optimum levels
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Water is lost: from the lungs through breathing, from skin as sweat, and in urine
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Negative feedback and stimulus’:
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Negative feedback is when the item being monitored deviates from the norm and the body then will
respond to get it back to normal
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A stimulus can be light, sound, touch, pressure, pain, a chemical, a change in position or
temperature
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Resect send this information to the coordination Centre
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The effectors respond to counteract the change and bring it back to optimum
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The nervous system:
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Stimulus - changes in the environment to which the body responds
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Sensory neurone - carries electrical nerve impulses from the receptors to the central nervous
system
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Motor neurone - carries electrical impulses from the central nervous system to the effectors
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Response - what happens as a result of a stimulus
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At each change there is a junction called a synapse where chemicals are released to cross the gap
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They bypassed the conscious part of the brain completely when a quick response is essential
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For example, in bright light, the pupil of the eye automatically gets smaller, so less light can enter
the eye, which stops them being damaged
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The key point in a reflex arc is that the impulse bypasses the conscious part of your brain
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It can
be affected by factors such as age, gender or drugs
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you should use the same person to catch the ruler each time
2
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the ruler should always be dropped at the same height
4
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Computers can give a more precise reaction time because they remove the possibility of human
errors from the measurement
2
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Using computers and removing the possibility that the person can predict when to respond, in the
ruler test the catcher may learn to anticipate the drop
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A nerve impulse arrives at the presynaptic cell
2
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The chemical diffuses across the synaptic cleft and binds to receptors on the next neurone,
triggering another impulse

The brain:
Information from sensory receptors all over your body feeds into your brain
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Your brain controls everything from walking to complex behaviours, as well
as your thoughts and feelings
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Cerebral cortex - consciousness, intelligence, memory and language
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Pituitary gland - processes chemical messengers called hormones to control menstrual cycle,
water and ion levels
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Cerebellum - coordinate muscular activity and balance (found at the back of your brain)
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To help us understand the brain we make observations about people
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Benefits of studying the brain:
1
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Surgery to remove part of the brain can help seizures which helps to treat epilepsy, if it’s not
controlled by drugs
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The brain is complex and delicate
2
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Brain functions involve many neurons and chemicals released by synapses
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There’s many ethical concerns with any studies carried out on living humans

The structure of the eye:
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Sclera - The tough outer layer of the eye
Cornea - transparent to let light into the eye and helps focus
Retina - contains light sensitive cells
Iris - Controls the size of the pupil
Pupil - The holes through which light enters the eye
Lens - A clear disc that focuses the light on the retina
Suspensory ligaments - holds the lens in place
Ciliary muscles - contract to change the shape of the lens
Optic nerve - carries impulses (via sensory neurons) to the brain from the retina

Very bright light can damage the retina therefore there is a reflex action to protect it
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In bright light:
1
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the circular muscles in the iris contract and the radial muscles relax

3
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In dim light, the radial muscles contract and the circular muscles relax
2
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therefore more light can enter
The ability to look at near and distant objects and example of a reflex action
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This is known as accommodation
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The ciliary muscles contract, this causes the suspensory ligament to slacking
b
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This increases the amount by which it refracts light
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Looking at distant objects:
a
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Lens becomes thin and less curved
c
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Eyeball too short
2
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Lens does not get fat enough to refract light enough
2
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the image on the retina is blurred
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solution:
1
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Eyeballs are too long
2
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Light is focused in front of the retina, not on it
2
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to wear glasses with a concave lens, a lens which curves inwards

Treatments to correct eyesight:
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Laser eye surgery:
Only available to adults
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To treat hyperopia, lasers are used to change the curve of the cornea so it refracts light to close objects
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They do the same as glasses, but can’t be seen
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Replacement lens surgery:
So shortsightedness you can add another lens inside the eye for permanent correction
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The endocrine system:
The system is a group of glands that release hormones into the body
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Hormones are carried in the
blood plasma but only have an effect on target organs
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1
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3
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1
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1
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1
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1
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3
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2
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The pituitary gland:
Controls growth in children
Stimulates the thyroid gland to make thyroxine to control the rate of metabolism
Stimulate ovaries to produce and release eggs, also to make oestrogen
Stimulate the testes to make sperm and testosterone
The pancreas:
Produces insulin
Used to regulate the blood glucose level
The thyroid:
Produces thyroxine
Regulates the metabolism, heart rate and temperature
The adrenal:
Produces adrenaline
Prepares the body for fight or flight response
The ovaries:
Produce oestrogen
Involved in the menstrual cycle
Controls the development of the female secondary sexual characteristics
The testes:
Produces testosterone
Control of puberty and sperm production
Involved in the development of the mail secondary sexual characteristics

Controlling blood glucose:
The pancreas monitors and controls blood glucose concentration
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2
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4
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2
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Cause: The pancreas doesn’t produce enough insulin
2
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Treatment (injection): Several injections a day or insulin to stop glucose levels getting too high
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Treatment (limited carbohydrates): spread intake of starchy carbohydrates throughout the day
5
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2
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4
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Solutions:
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Dialysis machine:
1
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Advantages:
1
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The body won’t reject it
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Can lead to infects and blood clots
2
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Patients have to control the diet
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Kidney transplant:
Uses a single healthy kidney from a donor

Advantages:
1
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Patient can eat what they want
3
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Cheaper in the long run
Disadvantages:

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3
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5
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7
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Oestrogent then inhibits further production of LH
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This
makes sure that no more follicles develop
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Progesterone inhibits further release of LH
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It
also makes sure the uterus lining isn't maintained if no embryo is implanted
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LH stimulates the ovary to release more oestrogen
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High oestrogen concentration triggers positive feedback to make ovulation happen
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2
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2
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FSH
it causes an egg to mature in an ovary
it stimulates the ovaries to release the hormone oestrogen
Oestrogen
it stops FSH being produced - so that only one egg matures in a cycle
it stimulates the pituitary gland to release the hormone LH
LH
causes the mature egg to be released from the ovary
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Prevents the
sperm entering the vagina
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98% reliable
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Female condom: a tube made of thin soft material closed at one end,which forms a lining to the
vagina
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Also helps protect against AIDS and STDs
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Combined pill: contains two hormones which stop ovulation (stop the ovaries from producing
eggs
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Can have side effects
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Progestogen only pill: contains one hormone (progestogen) it alters the lining of the womb and
causes changes in the cervical mucus
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99% efficient as long as taken at the correct time
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The hormone is slowly
absorbed into the body and works similarly to the combined pill
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Implant: small rods containing hormones are inserted under the skin in the upper arm
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Risks of side effects but 99% reliable
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The sperm are made
inactive by spermicide
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92-96% effective
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U
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Not suitable for all women
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Infertility:
This is when a couple can’t conceive naturally
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4
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2
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4
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FSH and LH are given to the woman to stimulate the maturation of multiple eggs
2
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The eggs are fertilised in a lab using the man’s sperm
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Once the embryos are formed one or two of them are transferred to the woman’s uterus
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A growth movement towards a stimulus is called a positive tropism
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Hormones coordinate a plant's response to the stimuli
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Hormones control growth of the shoots and roots, flowering and ripening of fruit
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Shoots grow away from the pull of gravity
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Roots grow towards the pull of gravity
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Phototropism:
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This is when a plant response to light
Positive phototropism is when the plant grows towards the light
Negative phototropism is when the plant grows away from the light

Inheritance, variation and evolution
Sexual reproduction:
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Meiosis
Two parents
Half of genetic information
Genetics are found in the sex cells or gametes
Requires a male and female gametes
Two gametes fuse creating a new individual
Offspring contains genetic information from both parents

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It introduces variation and variety
Quite slow and uses a lot of energy
Natural selection can occur

Asexual reproduction:
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One parent
No fusion of gametes
Produces genetically identical clones of the parents
Faster and uses less energy
One cell grows and splits into two
No variation
Examples: bacteria, small animals and plant cells, your body’s cell division

Sexual reproduction in a plant:
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Pollen and the egg cells are produced by meiosis
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Pollen from one flower must join the female part of another flower
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Plants are brightly coloured, scented and have large petals to attract animal pollinators eg
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Asexual reproduction in plants:
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A new plant grows due to mitosis
An example includes tiny new plants that form on the end of specialised stems called runners
New plants are formed even if flowers are destroyed by frost, eaten or fail to be pollinated
New plants are identical to their parent
No variation introduced

Fungi:
Asexually ●
Toadstools and puffballs produce spores asexually
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Many fungi are made up of a mass of thin threads called hyphae
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Sexually ●
Fungi reproduce sexually in poor, dry conditions
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The nuclei fuse
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To produce haploid spores again meiosis is used
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Human genome:
The entire genetic material of an organism
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DNA structure:
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The long strands of DNA are made by alternating sections of sugar and phosphate,
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attached to a base - A, C, G, T
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The base order controls the order in which acids are assembled, to form a protein
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A = adenine T = thymine G = guanine C = cytosine

Protein synthesis:
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The genes produce a protein template reflecting the base sequence
It leaves the nucleus and binds to a ribosome
The carrier molecules from the cytoplasm attach themselves to the template in the order given
The amino acids join together to form a specific protein
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Once complete, the chain folds up to form a unique shape enabling its function
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Non-coding DNA parts switch
genes on or off
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Variations in non-coding DNA
may affect gene expression and phenotype
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Mutations change the sequence of DNA bases
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Most mutations have little or no effect on the protein
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If the mutation occurs in the non-coding regions of the DNA, it can alter how genes are expressed
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Genetics - nature
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An organism’s characteristics are determined by the genes inherited from the parent
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The combination of the genes from two parents causes genetic variation
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If the mother smokes or drinks a lot of
alcohol, the baby can have a low weight
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Training can develop an athlete's muscles, as well as eating the correct diet can alter the athlete's
body
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Theories of evolution:
Charles Darwin:
‘ All living things that exist today and many more that are now extinct, evolved from simple life forms that
first developed more than 3 billion years ago
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The giraffes with the longest necks survived
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His theory wasn’t accepted because:
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Jean Baptiste Lamarck:
His theory was that the way organisms behaved affected the features of their body, therefore if an animal
used something a lot, overtime he thought it would grow and develop, and that organism change would be
passed on from parents to offspring
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The necks grow because they reach high to eat leaves
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Natural selection:
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Individual organisms with a species show variation because of differences in their genes
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The survivors pass on their genes to their offspring resulting in improved organism evolving
through natural selection
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Fossil records show the history of life on earth by the use of fossils
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They can show how different species evolved from common ancestors
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This has been caused by a chance mutation
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Bacteria with resistance have no
competition so survive and breeds
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Speciation:
A species is a group of similar organisms that can reproduce to give fertile offspring
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Speciation occurs when two populations of the same species become isolated due to geographical
barriers
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There is genetic variation in the isolated communities
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Over time the two populations changed so much that they can no longer interbreed
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