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Edexcel IGCSE Biology > Co-ordination and Response > Flashcards

Co-ordination and Response Flashcards

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1
Q

What is the state in which all internal conditions are kept constant in organisms called?

A

Homeostasis

These conditions must be kept constant through a number of processes to survive

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2
Q

Which physiological factors are controlled in mammals through homeostasis?

A
  • Body temperature
  • Water concentration
  • Glucose concentration
  • Blood pH
  • Levels of metabolic waste in blood
  • Carbon dioxide concentration
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3
Q

What are the four things which a co-ordinated response requires?

Coorindated responses can be to maintain homeostasis or to voluntarily coordinate a response such as moving

A
  • A stimulus (e.g. change in body temperature)
  • A receptor (e.g. receptor cells)
  • A co-ordination centre (e.g. brain or spinal chord which receives and processes information from receptors
  • An effector (e.g. muscle shivering) which brings about the response
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4
Q

What is the difference between a phototrophic response and a geotrophic response in plants?

A
  • A photrophism is a directional growth-response to the stimulus of light
  • A geotrophism is a directional growth-response to the stimulus of gravity
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5
Q

What are the phototrophisms which happen in plants and are the responses positive or negative?

A
  • Plants will grow their leaves towards the sun (to absorb more light for photosynthesis), this is a positive photrophism
  • Plants will grow their roots into the soil away from the sun, this is a negative phototrophism
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6
Q

What are the geotrophisms which happen in plants and are the responses positive or negative?

A
  • Plants grow their shoots up against gravity, this is a negative geotropism
  • Plants will grow their roots down (to anchor the plant and absorb nutrients), with gravity, this is a positive geotropism
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7
Q

What is auxin and what are its effects on plants?

A
  • Auxin is a growth regulator (similar to a hormone) which coordinates growth responses such as geotropisms and phototropisms
  • In shoots, auxin promotes cell elongation (so growth), in roots, auxin inhibits cell elongation (so less growth)
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8
Q

What determines auxin distribution in a plant and what happens to the plant as a result of this distribution?

A
  • In shoots, gravity causes auxins to be more concentrated in the lower side of the shoot, therefore stimulating growth in this area and causing the shoot to grow upwards
  • Also in shoots, light will cause auxins to collect on the shady side, stimulating growth in this area and causing the shoot to bend towards the light
  • In roots, gravity causes auxins to be more concentrated on the lower side, which inhibits growth in this area meaning the upperside will grow faster, causing the root to bend downwards towards the nutrients
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9
Q

What are the two control systems our body use to respond to stimuli?

A
  • The endocrine (hormonal) system
  • The nervous system
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10
Q

How does the encdocrine (hormonal) system work generally?

A
  • Chemical substances known as hormones are produced and released by glands
  • These hormones are carried by the blood and circulate the whole body
  • The are received by specific receptors and instigate a change on the target organ
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11
Q

What does the central nervous system consist of?

A
  • The brain
  • The spinal chord
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12
Q

What is the central nervous system linked to and what does that consist of?

A
  • It is linked to the peripheral nervous system
  • It contains all the nerves in the body

A nerve is a long chain of neurones

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13
Q

What are the three types of neurones?

A
  • Sensory
  • Relay
  • Motor
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14
Q

How does the nervous system work to carry out a response?

A
  • A stimulus is received by sensory neurones (in nerves)
  • When stimulated, the sensory neurone produces an electrical signal which travels along other sensory neurones (in nerves) to the co-ordinator (spinal chord or brain)
  • In the CNS, the electrical impulse is transferred to a relay neurone
  • The relay neurone links to a motor neurone, and along motor neurones the impulse travels until it reaches the effector, e.g. a muscle

Important: This is for an involuntary coordinated response, for moving, the brain sends an electrical signal to the muscles

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15
Q

Why are neurotransmitters needed?

A
  • The neurones do not come into direct compact to eachother, instead, the junction where the dendrites meet is called a synapse (where there is a small gap between the neurones)
  • Since the electrical impulse cannot jump the gap, it is briefly converted into a chemical messenger known as a neurotransmitter
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16
Q

How do electrical impulses pass from neurone to neurone?

A
  • An electrical impulse passes down the axon of the presynaptic neurone
  • This triggers vesicles at the end of the presynaptic neurone to release neurotransmitters which fuse with the presynaptic membrane and release the neurotransmitters into the cleft
  • The neurotransmitters diffuse across the synaptic cleft, and bind with the receptors of the post synaptic membrane
  • This stimulates the postsynaptic neurone to generate an electrical impulse, and the neurotransmitters are destroyed to stop more signals from being produced

  • Receptors have a complimentary shape to the neurotransmitters - drugs exploit this by binding to these receptors and stimulating certain impulses in our brain
17
Q

What is the cornea and what is its function?

A

The cornea is a transparent lens which acts as a guard for the eyes and contributes to optical power by refracting light as it enters the eye

18
Q

What is the iris and what is its function?

A

The iris the coloured part of the eyeball which controls the shape of the pupil to control how much light is let in

19
Q

What is the lens and what is its function?

A

The lens is a tranparent shield which can change shape to focus light onto the retina, creating a sharper image

  • The ciliary muscle is what changes the shape of the lens
  • The ciliary muscle is connected to the lens by suspensory ligaments
20
Q

What is the retina and what is its function?

A
  • The retina is a thin layer of tissue at the back of the eye which contains all of the receptor cells in the eye
  • Cone cells in the retina detect colour and rod cells detect light intensity

The fovea is the part of the retina with the highest density of receptor cells

21
Q

What is the optic nerve and what is its function?

A

A sensory neurone that carries electrical impulses stimulated by the light to the brain

22
Q

What is the pupil and what is its function?

A

A hole in the iris which lets light in

23
Q

How does the eye change when focusing on objects which are close up?

A
  • The ciliary muscles contract
  • The suspendory ligaments loosen
  • They then stop pulling on the lens, which causes it to become fatter/thicker
  • As a result, more light is refracted and we can focus on close objects
24
Q

How does the eye change when focusing on objects which are far away?

A
  • The ciliary muscles relax
  • The suspensory ligaments tighten
  • They pull on the lens, causing it to become thinner
  • As a result, less light is refracted and we can focus on far away objects
25
Q

How does the eye change when we are in a low-light environment?

A
  • Photoreceptors detect change in environment
  • Radial muscles in iris contract
  • Circular muscles in iris relax
  • Pupil dilates
  • More light enters the eye and visibility is improved
26
Q

How does the eye change when we are in a light-abundant environment?

A
  • Photoreceptors detect change in environment
  • Radial muscles in iris relax
  • Circular muscles in iris contract
  • Pupil constricts
  • Less light enters the eye to avoid retinal damage
27
Q

Where are the receptors and co-ordination centre for temperature?

A
  • Receptors are found peripherally on our skin and internally in our core
  • The thermoregulatory centre within the hyphothalamus is the co-ordination centre
28
Q

What is the process of sweating and how does it help us to cool down?

A
  • Sweat is secreted by the sweat glands onto our skin
  • The evaporation of the sweat from our skin uses heat energy from our body which cools us down
29
Q

What is the process of vasodilation and how does it help us to cool down?

A
  • Arterioles which supply blood to the capillaries in the skin increase the volume of blood flowing through these capillaries
  • They so do by relaxing the muscles in their walls, dilating the capillaries and allowing more blood to flow through
  • As a result, more blood flows through the capillaries in the skin and since blood carries heat energy, heat will radiate out of the skin, cooling us down

  • This process is the reason why people go red when hot
  • This process also occurs as a result of exercise to send more blood to the working muscles
30
Q

What is the process of vasoconstriction and how does it help to cool us down?

A
  • Arterioles which supply blood to the capillaries in the skin decrease the volume of blood flowing through these capillaries
  • They so do by contracting the muscles in their walls, constricting the capillaries and allowing less blood to flow through
  • As a result, less blood flows through the capillaries in the skin and since blood carries heat energy, less heat will radiate out of the skin, keeping us warm
31
Q

What other involuntary temperature control methods do we have?

A
  • Shivering to warm us
  • Erection of hairs to form an insulating layer of air, stopping heat radiation from the skin, keeping us warm
  • Relaxation of hairs to prevent this layer of air forming, cooling us down
32
Q

What are the effects of adrenaline?

A
  • Increase in heartrate and breathing rate to deliver oxygen and glucose to muscles
  • Diverting blood flow and vasodilation to send more blood to muscles
  • Breakdown of glycogen into glucose so glucose can be used in respiration
33
Q

What is the source, role and effect of insulin?

A
  • Insulin is responsible for maintaining homeostasis in our blood sugar levels
  • Cells in the pancreas detect an increase in blood glucose levels
  • This stimulates glands in the pancreas to release a hormone known as insulin
  • This hormone will stimulate the liver and muscles to take up the glucose and convert it into glycogen, reducing blood glucose levels at which point production of the hormone ceases

  • Glucagon is the opposite hormone, causing glycogen to be converted back into glucose
  • If glucose is too high, cells can lose water through osmosis and die due to low blood water potential, if glucose is too low, cells will not have the necessary reactants to respire

Edexcel IGCSE Biology (25 decks)

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