B3- ORGANISM LEVEL SYSTEMS (9-1 SPECIFICATION)

The Central Nervous System

• Made up of neurones
• Sensory receptors detect a change in the body's environment
• When a stimulus is detected by a receptor, the information is sent as impulses along neurones to the central nervous system.
• This then forms a coordinated response and the effector responds accordingly.

• Branched dendrites allow the neurone to connect with lost of other neurones.
• Fatty myelin sheath acts as an electrical insulator which speeds up the impulses.
• Neurones are long which speeds up impulses.
• The connection between neurones are synapses where transmitter chemicals diffuse across the gap and these then bind to receptor molecules in the membrane of the next neurone.

• Reflexes are automatic and are therefore faster than normal responses.
• The sensory neurone connects to the relay neurone which links to the motor neurone, the brain is missed out.
• Reflex actions are often carried out to protect outselves e.g. snatching your hand away from a burning plate.

    Cornea -> refracts light into eye

    Iris -> controls how much light enters pupil

    Lens -> focuses light on retina

    Ciliary muscles -> alter shape of lens

    Retina -> rods and cones detect light

    Optic nerve -> carries impulses from receptors to brain

Near Objects:

• Ciliary muscle relaxes, suspensory ligaments pull tight.
• Lens is less rounded so refracts less light.

Distant Objects:

• Ciliary muscle contracts, suspensory ligaments slacken.
• Lens is more rounded so refracts more light.

Long-sightedness:

• Occurs when the lens doesn't bend light enough or eyeball is too short.
• Images of near images brought into focus before retina.
• Corrected with a convex lens.

Short-sightedness:

• Occurs when the lens bends light too much or eyeball is too long.
• Images of distant objects brought into focus after retina.
• Corrected with a concave lens.

Cerebrum -> consciousness, intelligence, memory, language

Hypothalamus -> maintains body temperature, hormone production

Pituitary Gland -> hormone production

Medulla -> unconscious activity e.g. breathing, heart rate

Cerebellum -> muscle coordination

How do Scientists Study the Brain?

• Case studies
• fMRI scanners show what part of the brain is activated when taking part in certain activities.
• Examining brains of people who have died

Issues:

• Unethical to study without informed consent
• People need to donate their brains
• Case studies and fMRI scans are difficult to interpret because you don't know how the brain would react in a normal situation.

Treating the Brain:

• No way to repair damage to the central nervous system yet
• It's not possible to surgically remove brain tumours and surrounding parts may be damaged.

• Chemical messages sent in the blood which are then transported around the body
• They affect target cells which have receptors to respond appropriately

Adrenalin

• Prepares you for 'fight or flight' in stressful situations
• Released by adrenal gland
• Increases heart rate
• Increases blood flow and therefore increases oxygen and glucose levels for increased respiration
• Causes liver to break down glycogen and release glucose

Negative feedback -> occurs when your body detects a substance level is too high / low and your body triggers a response to get it back to normal again.

Stage 1 -> uterus lining breaks down and is released

Stage 2 -> uterus lining builds up from days 4-14 to a thick spongy layer

Stage 3 -> egg develops and is released around day 14

Stage 4 -> lining maintained for 14 days. If no fertilised egg is implanted into uterus wall then uterus lining breaks down again.

Hormones:

1. FSH -> causes egg to mature

2. Oestrogen -> causes uterus lining to thicken and grow

3. LH -> Stimulates egg release

4. Progesterone -> maintains uterus lining

• FSH and LH can be injected to stimulate ovulation.
• FSH and LH are also given before egg collection in IVF to stimulate egg production.

Progesterone contraceptives stimulate production of mucus at uterus opening,thicken lining and prevent ovulation. It can be taken as:

• Injections
• Implants into skin below arm
• Intrauterine System (plastic inserted into uterus)
• Mini-pill taken daily

Progesterone and Oestrogen contraceptives do all of the above:

• Combined pill
• Patch worn on skin

Barrier methods:

• Condoms (male and female)
• Diaphragm

Other methods:

• Natural methods
• Sterilisation (cutting / tying tubes in reproductive systems)

Risks:

• Hormonal methods have side-effects including heavy periods, acne etc.
• They could be carried out incorrectly
• Many methods involve medical input
• Only condoms can protect against STIs 

• Auxins are plant hormones which grow at tips of plant roots / shoots.
• It promotes growth in the shoot but inhibits growth in the root.
• Auxin accumulates on the shady side of the plant and causes the cells there to elongate. This makes the plant lean towards the light.

Plant shoots are positively phototropic (grow towards light and negatively gravitropic (grow away from gravity).

Plant roots are negatively phototropic (grow away from light) and positively gravitropic (grow towards gravity).

Gibberellin -> stimulates seed germination, stem growth, flowering

Ethene -> stimulates shedding of leaves, ripening of fruit

Uses:

• Selective herbicides only kill unwanted weeds in the soil usig specific auxins.
• Rooting powder contains auxins and allows you to grow plants from cuttings.
• Applying auxins and giberellins to unpollinated flowers produces seedless fruit.
• Treating seeds with giberellin alters dormancy.

Homeostasis -> maintaining a constant internal environment.

Controlling Body Temperature:

The Hypothalamus controls body temperature in order to ensure the body's enzymes can function properly.

Too hot:                                      Too cold:

- hairs lie flat                          - hairs stand on end

- sweat is secreted (energy               - muscles rapidly contract

  transferred to environment)              (shivering)

- Vasodilation involves more blood        - Vasoconstriction involves 

  flowing closer to surface to transfer     less blood flows near 

  more energy to surroundings.              surface (less heat lost)

Blood sugar too high:                  Blood sugar too low:

1. Insulin secreted by pancreas        1. Glucagon secreted by                                                  pancreas

2. Insulin makes liver turn glucose    2. Glucagon makes liver turn

   into glycogen                          glycagon into glucose

Type 1 Diabetes:

• pancreas produces little / no insulin
• genetic
• treated with insulin injections

Type 2 Diabetes:

• resistant to insulin
• caused by unhealthy lifestyle e.g. lack of excercise, obesity
• controlled with healthy eating, excercise, weightt loss etc.

• If water potential is higher outside cell, water will move into cell by osmosis and the cell will burst (lysis).
• If water potential is higher inside cell, water will leave cell by osmosis and cell will shrink (crenate).

Kidneys

• Kidneys control urine concentration, production and waste disposal.
• Kidneys contain millions of tubules or nephrons.

Inside the nephrons:

1. Blood flows at high pressure through glomerus, small molecules (e.g.     water, glucose) are filtered out into capsule.

2. Useful substances are selectively reabsorbed

3. Whatever isn't absorbed forms urine which is secreted by kidneys and     stored in the bladder.

• ADH is released by the pituitary gland to control urine concentration.
• The brain monitors water levels, instructs pituitary gland which releases more / less ADH, ADH makes kidney tubules more / less permeable to reabsorb more / less water.

Negative feedback is used to monitor water regulation.

Volume and concentration of urine varies:

Sweating and dehydration -> water loss so kidneys reabsorb more water, small volume on concentrated urine produced.

Excess water intake -> kidney excretes more water, lots of dilute urine.

High salt intake -> kidney excretes more salt, more concentrated urine.