Homeostasis

What is homeostasis?

The state of balance in the body when the temperature and other conditions are stable for cells and enzymes to work.

The regulation of internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.

Why does the temperature near the brain decrease when consuming cold water?

The blood is cooled in the mouth

Which flows to the brain

What should a runner do to reduce dehydration?

Drinks lots of water

To replenish water lost through sweating

What are the main internal conditions?

• Body temp

• Water levels

• Blood glucose levels

What are the features of the automatic control system?

What is the Nervous system?

CNS - central nervous system (brain & spinal chord)

Other nerves which run to and from CNS

What is a reflex arc?

1. Stimulus is detected by receptor

2. Electrical impulses travel along sensory neurones to the CNS

3. Reaches the synapse where a chemical is released

4. Diffuses to a relay neurone and triggers an electrical impulse which travels across relay neurone.

5. Reaches another synapse & another chemical released

6. Chemical triggers an electrical impulse in a motor neurone.

7. Electrical impulse travels down motor neurone to an effector

8. E.g. hand touches heat, skin (receptor) senses heat, effector (muscle) contracts and pulls hand away from heat (response).

What is a reflex?

• No decision making from the conscious part of the brain

• Automatic & rapid

• Protect us from danger

• E.g. removing hand from heat, protect face from object in flight

Reaction time Required Practical method

1. Person 1 sits on stool with dominant hand over table

2. Person hold meter ruler with 0 mark between P1 thumb and first finger

3. P2 drops ruler at random time

4. P1 must catch the ruler as fast as possible

5. Measure cm spot that the ruler was caught

6. Record on a table and repeat 10 times to calculate mean

7. Repeat with different people

Label this diagram of the brain

https://quizlet.com/gb/243958717/aqa-gcse-brain-diagram/

What are the functions of the different parts of the brain?

1. Cerebral cortex - language, memory and consciousness

2. Cerebellum - balance, co-ordinates movement

3. Medulla - Heart & Breathing rate

4. Hypothalamus - Thermoregulatory centre

5. Pituitary gland - coordinates many hormones

Why is it difficult to study the brain

• Tricky to access (skull)

• Complex structures (don’t know which parts do what)

• Extremely delicate (Easy to damage)

How do scientists study the brain?

1. Study patients who have brain damage (where damage is can be linked to its function)

2. Electrically stimulate brain and watch effects of peoples behavious (narrow down regions to functions)

3. MRI scan to see what part of brain is active during different activities

Label this diagram of the eye

What are the functions of different parts of the eye?

1. Cornea - Start focussing of light rays

2. Iris - Coloured part, controls pupil size

3. Pupil - Allows light into eye

4. Lens - Focus light rays onto back of the eye

5. Retina - receptor cells for light intensity & colour

6. Optic nerve - electrical impulses from eye to brain

7. Ciliary muscle & Suspensory ligaments - Work with lens to focus on near or far objects

8. Sclera - white part protects eye

How does the eye focus?

• Accommodation - The lens allows focus on near or far objects by changing its shape.

• The lens is surrounded by Circular (ciliary) muscles and fibres (suspensory ligaments.

• The ciliary muscle can contract or relax to change the thickness of the lens.

• When ciliary muscle contracts, suspensory ligaments loosen and the lens is now thicker and refracts light rays more strongly (close focus) vice versa.

How is long or short sightedness treated?

Hyperopia / Long sighted (Eyeball is too short, light focuses at point behind retina) - glasses with convex lens

Myopia / Short sighted (Lens too thick or eyeball is too long & light focuses at point in front of retina - Concave glasses lens

Laser surgery - changes shape of cornea

Or replace lens inside eye with artificial one.

Contact lenses

What is Thermoregulation? How is it done?

• Thermoregulatory centre is in the brain and controls body temp

• Contains receptors sensitive to temp of blood

• Skin also contains temp receptors and sends electrical impulses through sensory neurones to the thermoregulatory centre.

• Too hot:

  • Sweat glands release sweat onto surface of skin, sweat evaporates and takes energy from body.

  • Flushing - Blood vessels supplying capillaries dilate (get wider / Vasodilation) so more blood flows and heat can transfer out of blood.

• Too cold:

  • Blood vessels constrict (narrower/ vasoconstriction) So less heat is lost through blood.

  • Shiver - skeletal muscles contract, generate energy by muscles cells increasing rate of respiration.

  • Stop sweating

What is the Endocrine system?

• Number of glands which secrete hormones into blood stream. Blood carries hormones around body.

• Slower and longer lasting effect than nervous system

Label this Endocrine system diagram

What are the functions of the glands?

• Pancreas - Blood glucose concentration

• Ovaries & Testes - Puberty & reproduction

• Thyroid - Growth & Basal metabolic rate (How fast chemical reactions happen)

• Adrenal glands - release adrenaline when stressed

• Pituitary gland - Releases different hormones depending on conditions and act on other glands.

How is blood glucose concentration controlled?

• Carbs cause blood glucose concentration to rise.

• Pancreas senses this and produces hormone insulin.

• Triggers body cells to take glucose from blood.

• Triggers liver and muscle cells to store it as glycogen

• If blood glucose concentration falls too low, glucagon triggers liver cells to turn glycogen back into glucose into blood.

What is diabetes?

Type 1 - Pancreas doesn’t produce enough insulin. When carbs are consumed, the blood glucose rises but doesn’t go back down as far as it needs to

Type 2 - Body stops responding to the insulin produced. Must avoid carbs and exercise.

How does the body lose water?

1. Via lungs when we exhale

2. Sweat via skin (+ ions & urea)

3. Via kidneys in urine (+ ions & urea)

What do the kidneys do?

• Blood containing urea enters kidneys by arteries

• Removes excess ions, urea and water

• Leaves the kidneys as urine in bladder

• Blood leaves kidney through a vein

Explain this diagram

From kidneys to bladder

1. Blood passes through capilleries

2. Small molecules are filtered out (Urea, ions & water, glucose)

3. Pass into tube (yellow)

4. (Green arrows) Some of the molecules (not urea) are reabsorbed into blood (Selective reabsorption)

5. Urea, excess ions & excess water are released as urine.
   

How does the body deal with excess amino acids?

• Amino acids go into blood during digestion

• Liver breaks down excess amino acids into ammonia (Deamination)

• Ammonia is toxic so it it converted into urea

How does the body maintain water levels in blood?

• Increase water levels: The pituitary gland releases hormone ADH

• so more water can pass out of the kidney tubules to be reabsorbed into blood & less urine is produced

• Pituitary gland stops releasing ADH as water levels increase

• Decrease water levels: Pituitary gland stops releasing ADH, less water reabsorbed, more urine produced

What is kidney dialysis

• Kidney failure means blood contains too much urea, ions and water

• Kidney dialysis: patients blood passes over a semi-permeable membrane which allows smaller molecules through

• Dialysis fluid on other side of membrane - controls normal concentration of water and ions but no urea

• Steep concentration gradient lets smaller molecules pass through.

What are disadvantages of Kidney Dialysis and what is a better alternative?Compare them.

• Inconvenient - have to go to hospital several times a week

• Must eat a controlled diet

• Kidney transplant - Diseased kidney replaced with healthy kidney, but may be rejected.

The menstrual cycle

1. Ovulation (release of egg) every 28 days

2. To prepare, uterus lining becomes thick and spongy

3. Egg goes to uterus and can be fertilised if sperm is present, then implant into uterus wall, develop into a baby

4. If not fertilised, egg and uterus lining is released (period)

Hormones during the menstrual cycle

1. Follicle stimulating hormone (FSH) causes egg to mature in ovary

2. Luteinising hormone (LH) causses ovulation

3. Oestrogen (Produced by ovary) and progesterone maintain uterus lining incase egg is fertilised and implants.

How do the hormones interact with the menstrual cycle?

1. Pituitary gland releases FSH

2. FSH travels in blood to ovaries, causing egg to mature

3. FSH triggers ovaries to produce oestrogen, causing lining to become thick & stops pituitary gland releasing FSH

4. Pituitary gland release LH, triggers ovulation

5. Ovaries now produce progesterone, stops pituitary gland releasing LH and FSH to stop anymore eggs maturing or being released.

6. Progesterone also causes lining to become thick. progesterones falls if not fertilised, uterus lining and egg are released (period)

What is an IUD?

Intrauterine device (IUD) ‘coil’

• Prevents embryo from implanting

• Can release hormones to reduce risk of fertilisation

• Highly effective and can prevent pregnancy for up to 10 years

• DOesn’t protect agains STI’s

How does the pill work?

The pill - contains hormones which prevent the production of FSH which stops any eggs maturing. Highly effective if taken correctly (everyday)

Side effects: Risk of breast cancer, blood clots

What other hormone methods can a woman use for contraception?

Implant / Skin Patch / Injection, contains progesterone stopping the egg maturing or being released.

More convenient than taking a daily pill, has side effects

These don’t prevent STI’s or STD’s

What barrier methods are there?

Condom/Diaphragm: Barrier method stops sperm reaching egg, effective if used correctly.

Adv: no side effects

Disadv: condoms can break or slip off

More effective if used with a spermicide gel which kill or disable sperm.

What are surgical forms of contraception?

• Sterilisation

• Prevent women’s eggs reaching uterus

• Men: Prevents sperm leaving the penis.

• Difficult to reverse, be certain they don’t want children.

• Don’t protect against STI’s

What is the natural form of contraception?

• Abstain from sex after ovulation

• Hard to tell when ovulation occurs

• Doesn’t protect against STI’s

Opinions on contraception

• Some religions see it as unethical

• Some people think everyone should be able to choose for themselves.

• Condoms reduce risk of STI’s

What options are there to treat infertility?

• Fertility drug - injection of LH & FSH, ovulate more than usual

• IVF - fertilisation outside of body. First administer FSH & LH, eggs mature, collected, collect sperm and fertilise eggs in lab. Develop into embryos which are inserted into the womb.

• Not high success rates

• Emotionally stressful & Physically demanding on mum

• Lead to multiple births (risky for mum and babies)

• Ethical views: Destroying unwanted embryos

• Expensive

What is adrenaline?

Adrenal glands (On top of kidneys) release adrenaline in fear or stress. Released into blood. Increases heart rate to deliver more oxygen and glucose to body (Fight or flight)

What is thyroxine?

Thyroid gland in base of neck

Releases Thyroxine

Stimulates the basal metabolic rate (makes bodys chemical reactions take place faster)

Role in growth and development

What is a negative feedback loop?

What is phototropism, how was it investigated?

When plants grow towards the light.

1. Shine light onto shoots from one side

2. The shoots lean towards the light

3. When the tips of the shoot were cut off, they didn’t grow towards the light.

4. Suggested that the tips produce plant hormone auxin

5. Covered tips with foil, again didn’t grow to light so the tips are sensitive to light.

6. Covered bottom with foil and the tip still grew towards the light, so the bottom isn’t sensitive to light

How does a plant use auxin?

For Photopism:

1. Auxin produced at tip

2. Triggers cells growth

3. Light causes auxin to concentrate on darker side of shoot tip

4. Auxin spreads down the shoot

5. Cells on darker side grow faster than cells on light side, so tip towards the light.

For Gravitropism/Geotropism

1. Root grow towards force of gravity

2. Auxin produced in roots

3. Gravity causes auxin to concentrate on lower side

4. Auxin inhibits cell growth in roots.

5. Lower side grows slower than the upper side, so grow towards force of gravity

WHat other chemical are used in plants?

• Gibberellins - germination of seeds

• Ethene - controls cell division and fruit ripening

Plant Response RP (light) and variables

Investigate light intensity on height of seedlings

IV - light intensity

DV - Height

CV - Water volume

The full and partial light seedlings have similar heights because the chlorophyll is very efficient at absorbing light energy. They don’t need full light to grow

They tilted towards the light - phototropism

Darken ess - grew longest, when the seeds germinate, they grow rapidly to reach the light and in the darkness they continued grow rapidly to try and reach the light. Small yellow leaves, no energy for photosynthesis

Plant responses (light) RP Method

1. Cotton wool in 3 petri dishes, filled with equal volume of water

2. Place 10 mustard seeds in each dish

3. Leave in warm place to germinate

4. Water every day with same volume

5. Seeds will germinate

6. Ensure each sample has the same amount of germinated seeds

7. Measure height with ruler, hold stem to measure accurately.

8. Place one dish in full sunlight, one in partial light, one in darkness

9. Measure heights everyday for 5 consecutive days

10. Record results on table

11. Calculate mean seedling height per day

Plant responses (gravity) RP Method

1. Dish of seedlings placed on its side in the dark

2. Shoot grows upwards against direction of gravity

3. Roots grown down following direction of gravity

How are hormones used in agriculture and horticulture?

Auxins - weed killers, rooting powders, promoting growth in tissue culture

Gibberellins - Force a seeds to germinate before it normally would (end seed dormancy), encourage plants to flower, make fruit grown larger

Ethene - Ripen fruits just before sale.