B3 -Organism Level Systems

Question 1

What are the two types of nervous systems?

Answer 1

Central nervous system: the brain and spinal cord

Peripheral nervous system: other nerves and receptors that aren’t in the central nervous system.

Question 2

How does the nervous system coordinate a normal response?

Answer 2

1) A stimulus - change in the environment - is detected by a receptor
2) An electrical impulse is sent through the sensory neurone to the brain (In the CNS)
3) The brain coordinates a response to the stimulus
4) An electrical impulse is sent through the motor neurones to an effector - a muscle or gland - and a response is made.

Question 3

How are Neurones adapted for their function?

Answer 3

1) They have a long axon: this is for fast transmitting electrical impulses as it is faster than lots of small neurones.
2) The axons are surrounded in a myelin sheath: This acts as an electrical insulator speeding up the impulses
3) They have dendrites so they can connect to other neurones.

Question 4

What is a synapse and how do they work?

Answer 4

• Synapses are gaps between neurones and electrical impulses cannot pass therefore chemical messengers are used.

1) In the presynaptic neurone, chemical messengers called neurotransmitters are kept in tiny packages called vesicles
2) When there is an impulse in the presynaptic neurone the vesicles are pushed to the edge and they bind with the neurone’s membrane releasing the neurotransmitters into the synapse
3) The neurones diffuse from an area of high concentration to low concentration across the synapse and bind to receptors on the postsynaptic neurone
4) This generates a new impulse in the postsynaptic neurone

Question 5

What is a reflex action and how does it occur?

Answer 5

A reflex action: is a rapid and automatic action which doesn’t require conscious thought

1) Receptors detect a stimulus and an impulse is sent through the sensory neurone to the CNS (the spinal cord)
2) In the spinal cord a relay neurone sends this impulse back through a motor neurone to an effector (a muscle or gland) and a response is coordinated

Question 6

Features of the eye?

Answer 6

1) Cornea: refract (bends) light into the eye
2) Iris: Muscle which contracts or relaxes controlling how much light enters the eye
3) Lens: refracts light focusing it on the retina
4) Ciliary muscles and suspensory ligaments: alter the shape of the lens
5) Retina: light sensitive part of the eye
6) Rods: Sensitive to dim light, but can’t see colour
7) Cones: Can see colour, can’t see dim light well
8) Optic nerve: carries impulses from the retina receptors to the brain

Question 7

How does the eye change to see distant and near objects?

Answer 7

Distant:

1) Ciliary muscles relax, suspensory ligament contracts
- This results in less round shape to refract less light

Near:

1) Ciliary muscles contracts, suspensory ligament relaxes
- This results in more rounded shape to refract more light

Question 8

How does light work in people with long-sighted and short-sighted people? How is it fixed?

Answer 8

Long-sighted (Hyperopia):

• Light doesn’t refract enough or eyeball is too short so light meets behind the retina
• Convex lens used to fix it which refracts light converging rays onto the retina

Short-sighted (Myopia):

• Light refracts too much or eyeball is too long so light meets before the retina
• Concave lens used to fix it which diverges light rays to meet on the retina

Question 9

Features of the brain and their locations?

Answer 9

1) Cerebrum - the outer wrinkly part of the brain: responsible for consciousness, language, memory and intelligence
2) Hypothalamus - Under cerebrum: involved in body temperature maintenance and controlling the pituitary gland by releasing hormones
3) Pituitary - Under Hypothalamus: A gland responsible for releasing many hormones
4) Medulla - Bottom left of brain: Controls unconscious activities like breathing and heart rate
5) Cerebellum - Bottom right of brain: responsible for muscle coordination

Question 10

Why are there problems studying the brain?

Answer 10

1) Unethical as they might not be able to give consent
2) Nerves and neurones are hard to repair if damaged to can cause permanent brain damage
3) Studying brain of those who have dies required donations
4) Parts of the brain are hard to access

Question 11

What is an EEG and MRI scan?

Answer 11

EEG: related to record electrical activity of the brain and finding anomalies

MRI: uses magnetic fields and radio waves to produce a detailed image of the brain and spinal cord

Question 12

What is the endocrine system?

Answer 12

Made with glands which produce hormones

Question 13

What is a hormone?

Answer 13

These are chemical messengers which are secreted by glands into the blood and are detected by target organs.

Question 14

What is adrenaline and how does it work?

Answer 14

Adrenaline is a hormones which is responsible for the fight or flight response which increases the supply of oxygen and glucose

1) Adrenaline is secreted by adrenal glands and travel in the blood
2) Adrenaline binds to receptors on the heart causing heart muscles to contract more frequently and with more force - higher blood flow so more oxygen and glucose for increased respiration
3) Adrenaline binds to receptors on the liver causing liver to break down glycogen stores into glucose

Question 15

What is homeostasis?

Answer 15

Maintenance of constant internal living conditions in their optimum state

Question 16

What is Thyroxine and how does it show negative feedback?

Answer 16

Thyroxine is a hormone which is responsible for regulating metabolism - rate at which chemical reaction occur in the body

1) Thyroxine is secreted by thyroid glands as a response of TSH being released for pituitary gland
2) If the thyroxine levels are too high, the pituitary gland releases less TSH which signals the thyroid gland to release less thyroxine and levels drop
3) If the thyroxine levels too low, the pituitary gland releases more TSH, which signals the thyroid gland to release more thyroxine and levels increases

Question 17

5 sex hormones:

Answer 17

Testosterone: produced in testes and stimulated sperm production

Oestrogen: produced in the ovaries and causes lining of uterus to thicken and grow

Progesterone: Produced in ovaries and maintains the lining of uterus

FSH: produces in pituitary gland and causes egg to mature in one of the ovaries

LH: produced in pituitary gland and stimulates egg to be released (ovulation)

Question 18

Stages of menstrual cycle (without hormones named)?

Answer 18

1) Day 1: the uterus of lining breaks down
2) Day 4 - 14: The lining of uterus builds back up again to prepare for fertilised egg
3) Day 14: An egg develops and is released from an ovary (Ovulation)
4) Day 14 - Day 28: The lining of uterus is maintained and if there is no fertilised egg lining breaks down and cycle starts again. If there is a fertilised egg liling in continued to be maintained

Question 19

How do hormones contribute to menstrual cycle?

Answer 19

1) FSH is released and causes egg to mature in an ovary
- stimulates oestrogen production in ovaries

2) Oestrogen is released and causes lining to thicken and grow
- Stimulates LH production
- Inhibits FSH so only one egg is released

3) LH is released and stimulates release of egg from ovaries - ovulation
- indirectly stimulates progesterone production as progesterone produced by empty follicle in the ovary after the egg has been released.

4) Progesterone is released and maintains the uterus lining
- When there is low oestrogen levels and progesterone levels fall the lining breaks down
- Low progesterone stimulates FSH production and cycle restarts

Question 20

What is IVF and how does it work?

Answer 20

IVF - a fertility treatment where eggs are fertilised outside the body

• The woman is given FSH and LH to stimulate the production of more eggs than normal in ovaries
• Eggs are collected.
• Eggs are mixed with father’s sperm and grown into embryos
• one or two embryos are transferred into woman’s uterus

Question 21

3 types of contraception:

Answer 21

Hormonal: using the understanding of menstrual cycle and hormones to prevent fertilisation

Barrier: try stop sperm fertilising the egg

Natural: rely on not having sexual intercourse when the women is less fertile

Question 22

Types of hormonal contraception:

Think of some pros and cons

Answer 22

Injections(effective up to 3 months) and Mini-pills(taken every day):
-Hormones involved progesterone
HOW IT WORKS: Stimulates the production of thick cervical mucus making it less likely for sperm to fertilise egg and also thins uterus lining so fertilised egg from implanting.

Combined pill(taken in a 21 day pills, 7 day no pill cycle)
-Hormones involved progesterone and oestrogen
HOW IT WORKS: all the previous effects by also prevent ovulation by inhibiting FSH because of oestrogen

Question 23

Types of barrier contraception

Think of some pros and cons

Answer 23

Condom

Female condom

Question 24

What are plant growth hormones and where are they produced?

Answer 24

Auxin and is produced in tips of roots and shoots

• In shoots: promotes growth
• In roots: inhibits growth

Question 25

How does auxin cause roots and shoots to grow in a certain direction?

Answer 25

IN SHOOTS:
Shoots are positively phototropic (grows towards light):
- When shoot tip is exposed to light, auxin gathers on the shaded side promoting cell elongation on the shaded side and bending shoot towards light

Shoots are negatively gravitropic (grows away from gravity)
-When a shoot is growing sideways, auxin gaths on the lower side and causes lower side elongates faster than the top cells. The shoot bends upwards away from gravity.

IN ROOTS:
Roots are negatively phototropic (grows away from light)
-When root tip exposed to light, auxin gathers on the shaded side and inhibits cell elongation on the shaded side. The top grows faster than the bottom and root grows down away from light

Roots are positively gravitropic (grows towards gravity)
- When root is growing sideways, auxin gaths on the lower side. This prevents cell elongation at the bottom and the top grows faster at the top bending the roots downwards.

Question 26

Other different types of plant hormones?

Answer 26

Gibberellin: stimulates seed germination, stem growth and flowering

Ethene: stimulates shedding of leaves and ripening of fruits

Question 27

How does the body control body temperature?

Answer 27

1) Hypothalamus in brain has receptors sensitive to blood temperature .

When you are too hot:

• Erector muscles relax and hairs lie flat
• Lots of sweat excreted: when sweat evaporates it transfers energy from skin to the environment cooling you down
• Vasodilation: blood vessels near the skin surface dilate allowing more blood to flow close to surface of skin. Energy is transferred more from blood to environment

When you are too cold:

• Erector muscles contract and kairs stand up trapping an insulating layer of air to keep warm
• Very little sweat is produced
• Vasoconstriction: Blood vessel near the surface of skin constrict so less blood flows near skin surface and less energy transferred to environment
• Shiver: automatic contraction of muscles. Requires respiration which is an exothermic reaction releasing energy to warm body

Question 28

How does blood sugar levels rise and lower in day to day life?

Answer 28

Food containing carbohydrates put glucose into blood (increasing blood glucose levels)

Vigorous exercise uses glucose for respiration (decreasing blood glucose levels)

Question 29

How does the body control blood glucose levels?

Answer 29

Blood glucose levels too high:

1) Insulin is secreted from pancreas and it travels in the blood
2) The insulin is detected by the liver which signals liver to absorb glucose from blood and store it as glycogen
3) Blood glucose levels drop

Blood glucose levels too low:

1) Glucagon secreted from pancreas and travels in the blood
2) The glucagon is detected by liver and signal it ot release glycogen as glucose
3) Blood glucose levels increase

Question 30

What are the two types of diabetes and their treatments?

Answer 30

Type 1:
Pancreas secretes little or no insulin
Treatment: Injection of insulin

Type 2: The body cell of the person is unresponsive to the insulin produced
Treatment: healthy diet and regular exercise

Question 31

3 ways cells can react when in different water potentials?

Answer 31

This is important for body cells ->
1) If water potential outside cell is higher than the water potential inside cell water is drawn in via osmosis and may cause cell the burst - hypotonic

2) If water potential outside is equal to water potential inside the cell remains relatively the same - isotonic
3) If water potential out the cell lower than inside water is draw out of cell via osmosis and cell can shrink - hypertonic

Question 32

How does tubules work to form urine?

Answer 32

1) Blood flows at high pressures in the glomerulus (tight net of capillaries) and small molecules (water, sugar, salt and urea) are filtered into the bowman’s capsule
2) As liquid flows through tubules useful substances are reabsorbed:
- All sugars reabsorbed
- Sufficient sugar reabsorbed
- Sufficient water reabsorbed according to ADH levels
3) Whatever isn’t reabsorbed form urine and stored in bladder

Question 33

How does the body balance water content?

Answer 33

1) If water potential too high: The hypothalamus detects high water levels and signals the pituitary gland to release less ADH. This makes the tubule walls less permeable and less water reabsorbed into the bloodstream.
2) If water potential too low: The hypothalamus detects low water potential level and signal pancreas to release more ADH. The ADH makes the tubules more permeable so more water is reabsorbed into the blood.

Question 34

How does urine change depending of when it is hot?

Answer 34

When hot:
When there is loss of water (from things like sweating) ADH is released and tubules more permeable. This reabsorbs more water into blood. Urine is more concentrated as there is less water

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