B3 - Organism-level systems

Question 1

What are the 3 main stages to a nervous response?

Answer 1

Stimulus - a change in the environment
Receptors - a group of cells that detect the stimulus
Effectors - muscles or glands that respond

Question 2

What are the steps involved in a nervous reaction?

Answer 2

Stimulus -> receptor cells -> sensory neurones -> spinal chord -> brain -> spinal chord -> motor neurones -> effectors -> response

Question 3

What are the 3 types of neurones?

Answer 3

Sensory neurones - carry electrical impulses from receptor cells to the CNS (dendron transmits the impulse to the cell body)
Relay neurones - carry electrical impulses from sensory neurones to motor neurones (only found in CNS)
Motor neurones - carry electrical impulses from the CNS to effectors (axon transmits impulse away from the cell body)

Question 4

What is a reflex action?

Answer 4

Reflex actions are automatic (involuntary), they occur without thinking. By missing out the brain your body can react much faster

Question 5

Describe a reflex arc:

Answer 5

Stimulus -> Receptor cells -> Sensory neurone -> Spinal chord -> Motor neurone -> Effector -> Response

Question 6

Examples of reflex actions:

Answer 6

Burning your hand - your biceps contract so your hand pulls away

Exposure to sand in eyes - eyelid muscles contract making you blink

Question 7

Main structures of an eye:

Answer 7

Cornea - a transparent coating on the front of the eye that protects the eye and refracts light entering the eye
Pupil - central hole in the iris that allows light to enter the eye
Iris - a coloured ring of muscle tissue that alters pupil size by contracting or relaxing
Lens - a transparent biconvex lens that focuses light clearly onto the retina
Ciliary body - a ring of muscle tissue that alters the shape of the lens
Suspensory ligaments - ligament tissue that connects the ciliary muscle to the lens
Optic nerve - nervous tissue that carries nerve impulses to the brain

Question 8

How are images formed?

Answer 8

The cornea refracts incoming light rays. This provides most of the focus to the incoming light. The light then passes through the pupil and is further refracted by the lens which creates a sharp image on the retina. Photoreceptors in the retina produce a nervous impulse when exposed to light. This impulse travels down the optic nerve to the brain which interprets the impulse as a visual image.

Question 9

How does the eye focus on near and far objects?

Answer 9

• When you ciliary muscle contracts, your lens becomes more convex (fatter) and you can focus on nearby objects.
• When your ciliary muscles relax your lens becomes less convex (thinner) and you can focus on distant objects

Question 10

What causes short sightedness and how can it be corrected?

Answer 10

• Short sightedness is caused by a person’s lens being too strong or by the eyeball being too long. This means the light rays meet in front of the retina so the image is blurred.
• It can be corrected with a concave lens as it bends the light rays outward before they enter the eye

Question 11

What causes long sightedness and how can it be corrected?

Answer 11

Long sightedness is caused by a person’s lens being too weak, or by the eyeball being too short. This means that the light rays do not meet on the retina so image is blurred.

• It can be corrected with a convex lens which bends light rays inwards before they enter the eye

Question 12

What are the 2 types of photoreceptors?

Answer 12

Rods - These respond to light, and allow you to see in low light levels

Cones - These respond to different colours. Different cone cells respond to red, blue and green light

Question 13

What is the advantage of having a single brain?

Answer 13

Having a central control centre means neuronal communication is much faster than if control centres for different functions were spread around the body.

• The function of a brain is to process information and produce coordinated responses

Question 14

What are the 5 main areas of the brain and their functions?

Answer 14

Cerebrum -controls complex behaviour such as learning, memory, personality and conscious thought
Cerebellum - controls posture, balance and involuntary movements
Medulla - controls automatic actions such as heart and breathing rate
Hypothalamus - regulates temperature and water balance
Pituitary gland - stores and releases hormones that regulate many body functions

Question 15

How can you investigate brain function?

Answer 15

CT scans -use x-rays to create 3D images of inside the body, however can not be used regularly as x-ray radiation increases the risk of cancer

MRI scans - use powerful magnets to identify brain abnormalities

Question 16

What are the effects of damage to the PNS?

Answer 16

It can result in:

• an inability to detect pain
• numbness
• loss of coordination

However the PNS has a limited ability to regenerate and more severe nerve damage can be treated through surgery

Question 17

Why is it so difficult to repair the CNS and what are the effects of damage?

Answer 17

Can result in:

• a loss of control of body systems
• partial or complete paralysis
• memory loss or processing difficulties

The CNS cannot regenerate and it is extremely hard to do surgery:
- the spinal cord is extremely small so spinal injuries often lead to permanent disability

Some treatments for the brain are available such as:

• radiotherapy and chemotherapy - to treat a brain tumour
• surgery - to remove damaged brain tissue
• deep brain stimulation - inserting an electrode to stimulate brain function

Question 18

What are hormones and what do they do?

Answer 18

Hormones are chemical messengers that are secreted into the blood and made in endocrine glands. The blood transports the hormones in plasma around the body. Normally hormone responses are slow and long lasting however adrenaline is fast. Only target organs respond and hormones bind to specific receptors for that hormone.

Question 19

What is the endocrine system?

Answer 19

It’s the name given to all all the endocrine glands and the hormones they produce. It controls and coordinates body processes with the nervous system.

Question 20

Compare messaging using nerves and hormones:

Answer 20

Hormones - slower, in the blood, longer acting, larger area

Nerves - faster, electrical impulse along the axon of a neurone, short acting, very precise area

Question 21

What is thyroxine?

Answer 21

Thyroxine is a hormone released by the thyroid gland (found in neck). It plays a vital role in regulating the body’s metabolic rate(the speed at which the body transfers energy from its chemical store to perform functions).

Question 22

What is adrenaline?

Answer 22

The adrenal glands lie near your kidneys. They secrete the hormone adrenaline in times of stress preparing your body for intensive action by increasing heart rate, and activating processes that increase the supply of oxygen and glucose to cells

Question 23

What is the negative feedback loop?

Answer 23

• Conditions in the body change from set point
• Change detected by a receptor
• Corrective mechanisms activated by an effector
• Conditions returned for set point
• Corrective mechanisms switched off

Question 24

How are thyroxine levels controlled?

Answer 24

When the body requires more energy the hypothalamus sends an impulse to the pituitary gland to release TSH. TSH stimulates the thyroid gland to release thyroxine. This increases the metabolic rate allowing the cells to transfer additional energy.
Once the cells have the required energy the hypothalamus stops the production of TSH and the thyroid gland therefore stops releasing thyroxine.

Question 25

What is the menstrual cycle?

Answer 25

• lasts about 28 days
• prepares a woman’s body for a potential pregnancy
• lining of the uterus thickens while an egg matures
• ovulation occurs around the 14th day
• If the egg is fertilised it may implant the uterus lining
• If the egg is not fertilised the lining and egg are removed from the body which is known as a period

Question 26

Which 4 hormones control the menstrual cycle and their functions?

Answer 26

• Follicle-stimulating hormone (FSH) is secreted by the pituitary gland and causes an egg to mature and also stimulates the ovaries to produce oestrogen.
• Oestrogen is made and secreted by the ovaries and causes the lining of the uterus to build up. As oestrogen levels rise they inhibit the production of FSH to ensure only one egg matures and oestrogen also stimulates the pituitary gland to release LH
• Luteinising hormone (LH) is secreted by the pituitary gland. When LH levels reach a peak in the middle of the cycle ovulation is triggered
• Progesterone maintains the lining of the uterus and also inhibits LH so that only one egg is released

Question 27

What are non-hormonal methods of contraception and give 3 examples:

Answer 27

Non-hormonal are barrier methods that prevent sperm contacting the egg or physical devices that release chemical compounds which can kill sperm cells(spermicides) or prevent the implantation of a fertilised egg

Condom - inserted on top of a penis to prevent sperm from entering the vagina, can also prevent the spread of STIs

Diaphragm/Cervical cap - inserted into the vagina to cover the cervix, prevents sperm cells from entering the uterus, not effective unless used with a spermicide

Intrauterine device (IUD)/coil - inserted into the uterus and releases copper which prevents sperm surviving in the uterus and fallopian tubes and can also prevent implantation of a fertilised ovum, remains effective for 5-10 years

Question 28

What are hormonal methods of contraception and 3 examples?

Answer 28

Hormonal methods use hormones to disrupt the normal female reproductive cycle

Combined pill(oestrogen+progesterone) - Prevents ovulation, thickens mucus from the cervix preventing sperm from reaching an ovum and prevents implantation of a fertilised ovum. Taken daily for 21 days of the menstrual cycle

Progesterone pill - Thickens mucus from the cervix and maintains a thin lining for the uterus preventing implantation, can prevent ovulationMust be taken around the same time every day

Intrauterine system (IUS) - Inserted into the uterus and has the same affect as the progesterone pill. Remains effective for 3-5 years

Question 29

What are some causes of infertility?

Answer 29

• Blocked fallopian tubes
• Blocked sperm ducts
• Not enough sperm produced in testes
• Lack of mature eggs in ovaries
• Failure to release an egg

Question 30

What is fertility treatment?

Answer 30

Using hormones to try treat infertility conditions. FSH can be used as an artificial fertility drug as it stimulates eggs to be matured in the ovaries and increases oestrogen production which increases the likelihood of eggs being released

Question 31

How does in vitro fertilisation (IVF) work?

Answer 31

FSH and LH are given to the mother to ensure as many eggs as possible are matured and released so they can be harvested. They are then placed on a petri dish where they are mixed with a sample of the male’s semen which contains sperm cells. The eggs are checked if they are fertilised and early embryos are developing properly. When the fertilised eggs have formed tiny balls of cells 1 or 2 are placed in the woman’s womb and if everything is successful a baby will potentially be born

Question 32

Considerations around IVF:

Answer 32

• Expensive
• It’s not a natural process
• Many treatments result in multiple births which can be very dangerous

Question 33

What is phototropism and gravitropism?

Answer 33

Phototropism means growing towards the light. Plants stems are positively phototropic. As a stem grows towards the light it is able to photosynthesise more. This means more food for the plant so it’s able to grow faster.

Gravitropism is growing in the same direction as gravity. It is important for roots to grow downwards as it provides support and usually takes the roots closer to water

Question 34

What are auxins?

Answer 34

Auxins are plant hormones that enables a plant to grow towards or away from a stimulus.
Auxin is made in the cells near the tips of shoots or the roots. An uneven distribution in auxin causes a response to a stimulus.
Auxin promotes growth in shoots and inhibits growth in roots

Question 35

How do plants respond to light and gravity?

Answer 35

• When light hits one side of the shoot tip, auxin moves to the shaded part of the plant which builds up the auxin concentration there. The cells respond by elongating which increases the length of the shaded side causing the shoot to bend towards the light.
• Auxin gathers on the lower side of the root. Auxin inhibits growth in roots so the upper side grows more making it bend downwards in the direction of gravity.

Question 36

What are the three plant hormones and what are they used for?

Answer 36

Auxins - stimulate growth, used for weed killers, promoting root growth and delayed ripening.
Ethene - causes plant fruit to ripen by stimulating the conversion of starch into sugar, used for ripening fruit.
Gibberellins - They are used for controlling dormancy

Question 37

What happens when you get too hot?

Answer 37

The change in temperature is detected by the hypothalamus. Then:

• Body hairs lie flat to prevent an insulating layer of air being trapped
• Sweat glands start producing sweat. As the water in sweat evaporates heat energy from your body is transferred to surroundings which helps reduce temperature
• Capillaries near the surface of your skin widen which is called vasodilation which increases blood flow, increasing heat loss through radiation

Question 38

What happens when you get too cold?

Answer 38

The change in temperature is detected by the hypothalamus. Then:

• Sweat glands stop producing sweat
• Body hairs rise to trap am insulating layer of air
• Capillaries near the surface of your skin become narrower which is called vasoconstriction. There is less blood flow therefore reducing heat loss.
• Your body begins to shiver. This happens as the muscles contract and relax quickly, this makes cells respire faster transferring extra energy by heating.

Question 39

What is the normal body temperature?

Answer 39

37 degrees

Question 40

What happens if blood sugar levels are too high?

Answer 40

The pancreas detects this and releases the hormone insulin. Insulin travels in the blood to the liver. Insulin stimulates the liver to turn glucose into glycogen which is then stored in the liver. The pancreas then detects that the blood sugar levels are normal and stops releasing insulin

Question 41

What happens if blood sugar levels are too low?

Answer 41

The pancreas detects this and releases the hormone glucagon. Glucagon makes the liver turn glycogen back into glucose which is then released into the blood. The pancreas then detects that the blood sugar levels are normal and stops releasing glucagon

Question 42

What are the two types of diabetes and how can they be treated?

Answer 42

Type 1 - People with this cannot produce insulin. The condition normally begins in childhood. Is controlled with regular injections of insulin and the person should also have a balanced diet and exercise regularly.

Type 2 - People with this cannot effectively use insulin. The cells do not produce enough insulin or the cells do not respond properly to insulin. Occurs later in life and is linked to obesity. Controlled by a balanced diet and regular exercise.

Question 43

What are the capsule, medulla and cortex?

Answer 43

Capsule - outer membrane of the kidney, helps to shape and protect it from damage
Cortex - outer part of the kidney
Medulla - inner part of the kidney

Question 44

What happens inside a nephron as blood flows through?

Answer 44

Blood enters under high pressure through the glomerulus. The increased blood pressure forces small molecules such as water, glucose, salts and urea out of the capillaries and into the bowman’s capsule in a process called ultrafiltration. Then selective reabsorption occurs, as the filtrate moves through the tubule, all the glucose is reabsorbed and any water or salts that are needed. After this the filtrate passes through the loop of Henlé and the collecting ducts which reabsorb any more water if needed.

Question 45

What happens if the blood water potential is too high?

Answer 45

The hypothalamus detects the water potential is too high and sends an impulse to the pituitary gland to release less ADH. This makes the walls of the collecting duct less permeable to water therefore less water is reabsorbed back into the blood stream. This results in a large volume of dilute urine being produced.

Question 46

What happens if the blood water potential is too low?

Answer 46

The hypothalamus detects the water potential is too low and sends an impulse to the pituitary gland to release more ADH. This makes the walls of the collecting duct more permeable to water therefore more water is reabsorbed back into the blood stream. This results in a small volume of concentrated urine being produced.

Question 47

What are hypertonic, hypotonic and isotonic drinks?

Answer 47

Hypertonic - contains high levels of glucose and salts
Isotonic - contains ion concentrations of those equal in blood
Hypotonic - contains low levels of glucose and salts