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Biology (IGCSE) > B6: Responding to the environment > Flashcards

B6: Responding to the environment Flashcards

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1
Q

Describe a nerve impulse

A

An electrical signal that passes along nerve cells called neurons

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2
Q

Describe the human nervous system
in terms of

A
  • The central nervous system consisting of the brain and spine (CNS)
  • The peripheral nervous system (PNS)
  • The coordination and regulation of body functions
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3
Q

Identify motor(effector), relay(connector) and sensory neurons from diagrams

A

self-explanatory

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4
Q

Describe a simple reflex arc in terms of receptor, sensory neuron, relay neuron, motor neuron, and effector

A

stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response

Note: A reflex arc is super small, because it has the smallest number of synapses and neurons possible

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5
Q

Give an example of a common reflex arc

(*note: in a reflex action, an impulse is also sent to the brain, BUT the brain is NOT involved in coordinating the response)

A

Touching a hot object

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6
Q

Describe a reflex action

A

It is a means of automatically and rapidly integrating the coordination of stimuli with the responses of effectors (muscles and glands)

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7
Q

Distinguish between voluntary and involuntary action

A

Voluntary actions involve conscious thought (thinking time). That means the brain is responsible for coordinating the response of the effector.

In an involuntary action however it is the spine.

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8
Q

Question: Are reflex actions voluntary?

A

No, all reflex actions are involuntary as they do not involve conscious thought (thinking time) and happen very quickly to avoid unnecessary damage to the body.

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9
Q

Identify the structures of the eye limited to cornea, iris, pupil, lens, retina, optic nerve, ciliary muscles, suspensory ligaments, and blind spot

A
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10
Q

Whats the function of the cornea?

A

To refract light

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11
Q

Whats the function of the iris?

A

To control how much light enters the pupil

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12
Q

Whats the function of the lens?

A

To focus light onto the retina

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13
Q

Whats the function of the retina

A

Contains light receptors, some sensitive to light of different colours.
Rods detect light intensity, cones detect colour. Rods work well in dim light settings as well as normal light, however cones need a certain amount of light to distinguish colour and hence are not as good in dim light situations.

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14
Q

Function of the optic nerve

A

Carry nerve impulses to the brain

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15
Q

Explain the pupil reflex

A

The amount of light entering the eye is controlled by a reflex action . The size of the pupil changes in response to bright or dim light. This is controlled by the muscles of the iris.
- In dim light, the pupil dilates (widens) in order to allow as much light into the eye as possible to improve vision, the radial muscles contract, the circular muscles relax

  • In bright light, the pupil constricts (narrows) in order to prevent too much light from entering the eye and damaging the retina, the radial muscles relax, the circular muscles contract
  • There is an antagonistic action of circular and radial muscles.
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16
Q

Explain accomodation of the eyes

A

Accommodation is the process of changing the shape of the lens to focus on near or distant objects.

To focus on a near object – the lens becomes thicker, this allows the light rays to refract (bend) more strongly. ciliary muscles contracts, suspensory ligaments loosen (do NOT use the word relax as these arent muscles).

To focus on a distant object – the lens is pulled thin, this allows the light rays to refract slightly. The ciliary muscles relax, and and the suspensory ligaments tighten (do NOT use the word contracts as these aren’t muscles).

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17
Q

Define hormone

A

A chemical substance, produced by a gland, carried by the blood, which alters the activity of one or two target organs.

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18
Q

Describe Adrenaline and its effects

A

adrenaline is the hormone released in ‘fight or flight’ situations.

The only effects that need to be known are:
- increased breathing rate
- increased heart/pulse rate
- pupil dilation

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19
Q

Discuss the role of the hormone adrenaline in the chemical control of metabolic activity including increasing the blood glucose level and pulse rate

A
  1. Adrenaline controlling blood glucose level
    Adrenaline stimulates the liver to break down glycogen into glucose. This is released into the blood stream.
    Adrenaline (also known as epinephrine) is a hormone produced in the adrenal gland. It is released when the body is under acute stress or during exercise.
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20
Q

Compare the nervous and hormonal control system in terms of speed and longetivity

A

Nervous system:
- very fast speed of transmission/action
- Message format: Electrical message
- Examples of processes controlled: Muscles and glands
- Duration of response: Short-lived,

Hormonal system:
- Slower transmission/speed of action
- Message format: Chemical substance carried in blood
- duration of response: Larger
- Examples of processes controlled:
Growth and metabolism

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21
Q

Define gravitropism

A

A response in which parts of a plant grow towards or away from gravity.

Note: Gravitropism used to be called geotropism

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22
Q

Define phototropism

A

A response in which parts of a plant grow towards or away from the direction from which light is coming.

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23
Q

Provide an example of the chemical control of a plant growth

A

Phototropism and gravitropism of shoots

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24
Q

Explain the role of auxin in controlling shoot growth

A
  • Auxin in made in the shoot tip (only)
  • Auxin spreads through the plant from the shoot tip
  • Auxin is unequally distributed in response to light and gravity
  • Auxin stimulates cell elongation

In phototropism:
- auxin moves to the side away from the light
- causing the side away from the light to grow more than the side facing the light
- thus making the the plant bend towards the light

In gravitropism:
The plants gather on the lower side of the plant.

(these regions = the shoot tip?) These regions are called ‘meristems’. More specifically, a meristem is a region of cell division in a plant

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25
Q

Investigate gravitropism and phototropism in shoots and roots

A

In the shoot the chemical (auxin) stimulates growth so the stem grows upwards. So stems have negative gravitropism (they go in the opposite direction of gravity.

In the root auxin slows growth, so the root grows downwards (positive gravitropism)

Think of it like this: When a stem is placed horizontally, the bottom side contains more auxin and grows more - causing the stem to grow upwards against the force of gravity. In a root placed horizontally, the bottom side contains more auxin and grows less - causing the root to grow in the direction of the force of gravity.

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26
Q

Define homeostasis

A

The maintenance of a constant internal environment

27
Q

Name and identify on a diagram of the skin: hairs, hair erector muscles, sweat glands, receptors, sensory neurons, blood vessels, and fatty tissue

A
28
Q

Describe the maintenance of a constant body temperature in humans in terms of insulation, sweating, shivering and the role of the brain (limited to blood temperature receptors and coordination)

A

Humans maintain our body temperature at 37oC.

Fat is an insulator, so when the external temperature fluctuates, it prevents our internal temperature from similarly fluctuating. This is because it traps heat inside our body and slows down the warming up of our body from an external source.

When the temperature changes, temperature receptors in the skin detect this information and send it as impulses through nerves to a part of our brain called the hypothalamus. This part of our brain is in charge of maintaining constant body temperature – it works like a thermostat.

It sends electrical impulses along nerves to body parts that help regulate body temperature.

When the temperature rises, the hypothalamus stimulates:

1) Hair to lie flat – the hair erector muscle is relaxed, allowing the hair to lie flat against the skin, so no air is trapped close to the skin, so we are insulated less. This is less effective in humans as we do not have as much body hair/ fur as some animals.
2) Vasodilation – the muscles in the walls of the arterioles supplying skin-surface capillaries relax, increasing the size of the arteriole lumen. More blood flows, so more heat can be lost to the environment from the blood at a time.
3) Sweating – sweat is secreted by sweat glands. It evaporates, taking heat from the skin with it, causing the body to cool down.
4) Metabolism slows down – metabolism usually consists of exothermic reactions (reactions that give off heat energy) so slower metabolism means less heat is given off at a time.

When the temperature falls, the hypothalamus stimulates:

1) Hair to stand erect – the erector muscle contracts, pulling the hair to stand up straight. This allows the hair to trap air close to the skin. As air is an insulator, it traps heat close to the skin, warming up the body.
2) Vasoconstriction – muscles in arteriole walls contract, making the lumen smaller, so less blood travels through the skin at a time, reducing the heat loss per unit time.
3) Reduces sweating – so less sweat evaporates, making the body cool down less.
4) Metabolism may increase.
Shivering – muscles in some part of the body involuntarily contract and relax very quickly, producing heat as a result.

29
Q

Describe how vasoconstriction, shivering, and hairs are used to regulate body temperature

A
30
Q

How is heat lost on the skin surface from blood passing through it

A

The heat (from blood) is lost through radiation

31
Q

Explain that homeostasis is the control of internal conditions within set limits

A

g

32
Q

Explain the concept of control by negative feedback

A

Negative feedback is when a fluctuation in a particular parameter, such as body temperature, is reduced so that it returns to its normal range of functioning by triggering a sensor that stimulates a response in an effector that reduces the fluctuation. In other words, any change is counteracted so that it returns to its set-point.

Examples of negative feedback systems include thermoregulation (control of body temperature), blood glucose concentration, osmoregulation (control of blood water potential), etc. This is because any changes in any of these parameters result in the body acting so that the change is minimised and is brought back to its normal range.

33
Q

Describe the control of the glucose content of the blood by the liver and the roles of insulin and glucagon from the pancreas

A

The hormones insulin and glucagon, secreted by the pancreas, control the level of blood glucose. The hormones travel to the liver in the blood, which is the organ that controls blood glucose levels.

Glycogen is a short-term storage molecule. It is a polymer made of glucose molecules.

When the blood glucose level increases above its set point:

The pancreas secretes insulin, which travels to the liver in the bloodstream. Insulin stimulates liver cells to absorb glucose and stimulates the conversion of glucose to glycogen. Insulin also encourages an increase in the rate of respiration – this means more blood glucose is taken up by cells and respired. All of this reduces blood glucose levels.

When the blood glucose level decreases below its set point:

Glucagon is secreted by the pancreas, which then travels to the liver via blood. The hormone glucagon stimulates the conversion of glycogen to glucose (this process is gluconeogenesis), and glucose is released back into the bloodstream. This increases blood glucose levels.

34
Q

Describe the maintenance of a constant internal body temperature in humans in terms of vasodilation and vasoconstriction of arterioles supplying the skin surface.

A

When we are cold blood flow in capillaries slows down because arterioles leading to the skin capillaries get narrower - this is known as vasoconstriction
This reduces the amount of heat lost from blood by radiation as less blood flows through the surface of the skin
When we are hot blood flow in capillaries increases because blood vessels to the skin capillaries get wider - this is known as vasodilation
This cools the body as blood (which carries heat around the body) is flowing at a faster rate through the skin’s surface and so more heat is lost by radiation

35
Q

provide 2 examples of an effector

A

muscles and glands

36
Q

Why do animals need fast and efficient communication between their receptors and effectors?

A

Most animals move in search of food. Many animals need to be able to move very quickly to catch their food and to avoid predators.

37
Q

What is coordination?

A

The way in which receptors pick up stimuli and then pass information onto effectors.

38
Q

What are the two methods of sending information from receptors to effectors?

A

Through nerves, or through hormones (hormones are a part of the endocrine system)

39
Q

What is the CNS made up of?

A

Brain and spinal chord

40
Q

What is the PNS made up of?

A

Nerves and receptors. Essentially the peripheral nervous system includes all of the nerves that branch out from the brain and spinal cord and extend to other parts of the body, including muscles and organs.

41
Q

What is the role of the CNS?

A
  • made up of neurons
  • coordinates information travelling through the nervous system
  • brain/spinal chord receive electrical impulses and send an impulse on, along the appropriate nerve fibres, to the appropriate effector
42
Q

Explain the reflex arc

A
  1. Sensory receptor detects the stimuli
  2. Receptor generates a nerve impulse which travels to the spinal chord along the axon of a sensory neuron
  3. In the spinal chord, the neuron passes an impulse onto numerous other neurons (these neurons are called relay neurons)
  4. The relay neurons pass this impulse onto the brain, as well as an effector
  5. The impulse travels to an effector along the axon of a motor neuron
43
Q

Provide a very famous example of a reflex action

A

The knee jerk reflex is an example of a reflex action. A sharp tap just below the knee stimulates a receptor. This sends impulses along a sensory neurone into the spinal cord. The impulse then travels along a motor neurone to the thigh muscle, which quickly contracts and raises the lower leg.

44
Q

Motor neuron (recognise the parts on a diagram and explain what they are/what they do)

A

Axon:
- Extended cell body
- function: transmit electrical impulses

Dendrites:
- Helps make connections with other neurons by forming synapses
- Synapse = junction between neurones

Myelin Sheath
- Made of fat
- Acts as an insulator
- Prevents loss of information

Node of ranvier:
- Region where there is no myelin sheath over the axon
- signals can jump between nodes; allows quick transmission of impulses

45
Q

Sensory neuron - recognise parts of a diagram and their functions (sensory neuron sends info from receptors to the CNS)

A
46
Q

Relay neuron (recognise from diagram)

A
47
Q

Explain the difference between the PNS and CNS in terms of neurons

A

Even though this picture is conceptually correct, for some reason the igcse say that motor neurons are a part of the CNS, sensory neurons a part of the PNS, and relay neurons a part of brain/spinal chord

48
Q

What are the two types of reflex actions and give an example of each:

A

Spinal reflex action:
- e.g. knee jerk reflex
- e.g. touching hot object below the neck

Cranial reflex:
- e.g. pupil reflex

49
Q

Name 5 sensory organs

A
  • Eyes
  • Nose
  • Ears
  • Skin
  • Tongue
50
Q

Describe the functions of the parts of the eye

A

Cornea:
- Transparent layer
- refracts light rays
- fixed shape

Iris:
- Middle = gap = pupil
- Controlled by antagonistic muscles (circular and radial muscles)
- The iris contains pigments which stop light passing through to the retina

Lens:
- Biconcave shape
- Refracts/focuses light rays even more onto focal point/fovea (accomodation)

Retina (light sensitive layer):
- Rod cells (very sensitive to low intensity light rays; dark
- Cones (High intensity light rays = colour)
- These send electrical impulses to the optical nerve

Fovea:
Only has cone cells = high resolution images

Blind spot:
Has no rod or cone cells

Optic nerve:
- Transmits impulses from our retina (the receptor) to the brain
- the brain sorts out all the impulses from the receptor cells, and builds up an image

Choroid layer:
- prevents internal reflection of light rays
- dark pigmented layer
- dark = poor emitter
- The choroid is behind the retina; it absorbs all light once it has passed through the retina so it cant be scattered around again

Sclera:
- white layer
- prevents mechanical injury from e.g. dust
- contains blood vessels; carries nutrients into the fluids in the eye
- Only the sclera and choroid have blood capillaries, because if blood were supplied to other parts of the eye it would absorb light and not let it pass through

Vitreous humour:
- between the lens and retina
- supports the eyeball (kinda like a inflated the balloon that helps everything hold its shape)

Aqueous humour:
- Between cornea and lens
- Has salts which can nourish the lens

51
Q

Why does the pupil reflex exist?

A

Light of high intensities can damage our retinas by damaging the receptor cells on it

52
Q

Hormones are made in ________ ____, which secrete the hormones directly into ____ ___________, and the hormones are dissolved in the ____ ________

A

Endocrine glands,
Blood capillaries,
Blood plasma

53
Q

Why does the liver destroy hormones?

A

If not they would keep circulating and triggering the same actions

54
Q

Why does adrenaline cause the changes which it causes?

A

There is an adrenal gland above each kidney which secrete adrenaline.

1) increased heart rate (target organ: heart)
- supplies more oxygen to brain and muscles
- more energy to fight or run away with
- supply O2 for aerobic respiration when running away

2) Pupil dilation (target organ: Iris)
- Allows more light to enter eye
- Can see danger more clearly

3) Increased breathing (target organ: lungs) - more O2, less CO2 in system

4) Increase sweating (target organ: sweat glands)
- cool down body temperature

5) Adrenaline can cause the blood vessels in your skin and digestive system to contract so that they carry very little blood. This makes you go pale and give you ‘butterflies in your stomach’. As much blood is needed for your brain and muscles in the emergency.

6) Adrenaline can also cause the liver to convert glycogen into glucose and release it into the blood stream. This provides extra glucose for the muscles which can release energy from it (in respiration) and use the energy for contracting.

55
Q

What glands do you need to know (+what is secreted from them)

A
  • pancreas: glucagon, insulin
  • adrenal gland: adrenaline
  • Ovaries:
    Estrogen, Progesterone
  • Testes: Testosterone
56
Q

What is a tropism?

A

A growth response by a plant in which the direction of the growth is affected by the direction of the stimulus.

57
Q

Why must shoots grow upwards (away from gravity and towards light)?

A

So that the leaves are held out to sunlight, the better they can photosynthesise. Flowers too need to be held up in the air, where insects, birds or the wind can pollinate them.

58
Q

How does auxin going onto one side cause growth?

A

The plant hormone auxin is well known to stimulate cell elongation via increasing wall extensibility.

59
Q

Under even light auxin will cause the shoot to grow _____ ___.

However, under unidirectional light Auxin will cause the shoot to grow towards the ______ _____, as auxin prefers the shady side.

A

straight up,

light side.

(Look at pg 1115 of the text book to understand this question, bottom-right)

60
Q

Cognito video on phototropism and geotropism:

A

https://www.youtube.com/watch?v=rKHIfsHX1aA

61
Q

Homeostasis - read from pg 116 of the text book

A

Additional thingies

62
Q

what is in charge of controlling all temperature mechanisms in the body?

How does it do this?

A

1) The hypothalamus
2) It has temperature receptors which sense the temperature of blood running through it

63
Q

Why is it that when you’re talking about the suspensory ligaments you always use the words “slacken” and “taut” and not “contract” and “relax”?

A

Because they aren’t muscles in themselves, the suspensory ligaments cannot contract and relax.

64
Q

1) Past paper questions + quizlets

2) Divesh past paper questions

A

1) https://docs.google.com/presentation/d/1fB6mAdIXNUApaPes1FQriJ2V07TM_ErtAOGupuK4N04/edit#slide=id.g731bac0daf_0_6

2) https://drive.google.com/drive/u/0/folders/13gqW4XsJdMorgQ_TsJxOYZp2RyjzPhA2

Biology (IGCSE) (6 decks)

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