What is the purpose of the nervous system?
To enable humans to react to their surroundings and coordinate their behaviour
Name the five sense organs and their receptors.
- Eyes : light receptors
- Ears : sound receptors, balance receptors (detecting change in position)
- Nose : smell receptors
- Tongue : taste receptors
- Skin : touch, pressure, pain and temperature change receptors
A fast automatic response of the body to a potentially dangerous stimulus
What is the CNS?
A system consisting of the brain and spinal cord where all the information from sense organs is sent and where reflexes and actions are coordinated.
Describe the reflex arc.
- Stimulus detected by receptor
- Impulses sent along sensory neurone
- Impulse reaches synapse
- Electric impulse in relay neurone
- Impulse reaches synapse
- Electric impulse in motor neurone
- Impulse reaches effector
What happens at a synapse?
- The nerve signal is transferred by chemicals which diffuse across the gap
- The chemicals set off a new electrical signal in the next neurone
A connection between two neurones
Chemical messengers which travel in the blood to activate target cells, co-ordinating many processes in the body.
Where are hormones produced?
What is the difference between a nerve and a hormone?
- Nerve = fast action vs Hormone = slower action
- Nerve = act for a short time vs Hormone = act for a longer time
- Nerve = act on a precise area vs Hormone = act in a more general way
What is the function of LH and where is it produced?
- Pituitary gland
- Stimulates ovulation
What is the function of oestrogen and where is it produced?
- Causes pituitary gland to produce LH
- Inhibits further release of FSH
What is the function of FSH and where is it produced?
- Pituitary gland
- Stimulates egg maturation
- Stimulates ovaries to produce oestrogen
What is the function of progesterone and where is it produced?
- Maintains uterus lining
Name 2 functions of the uterus
- Feeds foetus
- Protects foetus
What period is stage 1 of the menstrual cycle and what happens?
Day 1 - 4
Lining of the uterus breaks down
What period is stage 2 of the menstrual cycle and what happens?
Day 4 - 14
Lining of the uterus builds up
What period is stage 3 of the menstrual cycle and what happens?
An egg is released
What period is stage 4 of the menstrual cycle and what happens?
Day 14 -28
The lining of the uterus is maintained
A substance preventing conception
What do modern pills contain lower doses of oestrogen?
There were concerns about links to dangerous side effects e.g blood clots
What two hormones do modern pills contain and why?
- Progesterone: stimulates the production of thick cervical mucus stopping sperm reaching the egg
- Oestrogen: inhibits production of FSH (no more egg maturation)
What are the advantages of the pill?
- Over 99% efficient at preventing pregnancy
- Reduces risk of some cancers
What are the disadvantages of the pill?
- Isn’t 100% efficient
- Side effects e.g headaches, irregular menstrual bleeding
- Doesn’t protect against STDs
What two hormones are injected as fertility treatment?
What are the disadvantages of fertility treatment?
- Doesn’t always work
- Too many eggs could be stimulated
What is homeostasis?
The maintaining of a constant internal environment
What does the body control?
- Ion content
- Water content
- Sugar content
Where do ions in the body come from?
Absorbed into the blood from food
How are excess ions removed?
By the kidneys in urine and sweat
How is water lost?
Via the skin when we sweat, the lungs when we breathe, and the kidneys in urine
Why is temperature maintained at 37c degrees?
To maintain the temperature at which enzymes work best
Why do blood sugar levels need to be controlled?
To provide the cells with a constant supply of energy.
Explain how shoots respond to light.
- When the shoot tip is exposed to light, more auxin accumulates on the side in shade than light.
- This makes cells grow faster in the shaded side so the shoot bends towards light.
Explain how shoots respond to gravity.
- When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.
- The lower side grows faster, bending the shoot upwards.
Explain how roots respond to gravity.
- A root growing sideways has more auxin on the lower side.
- Cells on the top grow faster (the bottom ones are inhibited by the auxin) and the roots bend downwards.
Explain how roots respond to moisture.
- More auxin on the side with moisture
- Inhibits growth on that side, causing the root to bend in that direction - towards the moisture.
What is the plant growth hormone and where is it produced?
- Produced in the tip
What does auxin do in roots and shoots?
- Roots: inhibits growth
- Shoots: promotes growth
How does a shoot with the tip cut off grow?
- No auxin available
- Shoot won’t grow
How does a shoot with the tip covered grow?
- Auxin will stay in the shade, so in the tip where it is produced
- Causes elongation behind the tip causing the shoot to grow
Explain the process of IVF
- FSH and LH are given to stimulate egg production
- Eggs are collected from the ovaries and fertilised in the lab using a man’s sperm
- Once the embryos are tiny balls of cells, one or two are transferred to the woman’s uterus.
What are the arguments for IVF?
- Allows couples who have difficulty conceiving children - one biologically their own.
- Allows women who have difficulty conceiving the experience of pregnancy and bond with the child.
What are the arguments against IVF?
- Too many children in adoption centres
- High cost to NHS (could be spent on something else)
- Could lead to designer babies (embryos can be screened)
- Strong reactions to hormones e.g vomiting
- Risk of multiple births and miscarriages
Describe two uses of plant hormones in agriculture.
- Weedkillers : they only disrupt the growth of weeds
- Rooting hormones : ensuring plant cuttings grow in soil