5:1:5 Plant and Animal Responses Flashcards
1
Q
What are plant responses, and examples
A
- Responses to abiotic or biotic environmental stimuli, in order to provide the plant with selective advantages
- Tropisms
- Responses to tough
- Responses to herbivory
- Responses to abiotic stress
2
Q
What are tropisms, and examples
A
- A growth movement of a part of a plant in response to a directional stimulus, movement can be towards or away the stimulus
- Phototropism
- Geotropism
- Hydrotropism
- Thigmotropism
- Chemotropism
3
Q
What is phototropism
A
- Response to the abiotic stimulus of light
- It ensures plant gets access to as much light as possible to maximise photosynthesis
4
Q
What is geotrophism
A
- Response to the abiotic stimulus gravity
- Shoots show negative geotropism and roots show positive geotropism, ensuring that roots/shoots grow in the right direction regardless of seed orientation
5
Q
How do plants respond to touch with example
A
- Leaflets of the Mimosa pudica fold in when touched
- The response isn’t related to direction so isn’t a tropism
- Movement occurs rapidly, and is an adaptation to protect the leaves from herbivory or to reduce transpiration
6
Q
How do plants respond to herbivory
A
- Many plants produce herbivore-repellent chemicals in response to damage or stress
- Examples are tannins, alkaloids, pheromones
7
Q
How do alkaloids produced by plants protect them from herbivory, and examples
A
- The nitrogenous compounds are bitter tasting and can be toxic to herbivores
- e.g. Caffeine and nicotine
8
Q
How do pheromones produced by plants protect them from herbivory
A
- Chemicals released by members of species that affect the physiology or behaviour of other species
- May be directly toxic to herbivores or trigger other chemical defences
9
Q
How do plants respond to abiotic stress
A
- Abiotic stress includes freezing, drought, increased soil salinity
- Plants respond to drought by deducting water loss and shutting their stomata or by dropping their leaves
- Some plants contain an antifreeze chemical that decreases the formation of ice crystals
10
Q
Describe Darwin’s experiment to observe phototropism and what it shows
A
- Darwin discovered that removing the tip of a coleoptile stopped the phototropic response to a undirectional light source
- To ensure this wasn’t just from wounding to the plant, he covered the top of other coleoptiles with opaque caps, which also stopped the phototropic response
- This shows the tip of the coleoptile is responsible for detecting light
11
Q
Describe Boysen-Jensen’s experiment to observe phototropism and what it shows
A
- He found that is he replaced the cut coleoptile onto the plant with a gelatine block between, the phototropic response was restored
- This shows that the stimulus for growth was a chemical hormone
- Then he replaced the gelatine with a mica barrier (impermeable to chemicals) on the lit side, and the phototropic response occurred
- When he placed the mica on the unlit side, the phototropic response didn’t occur
- This shows that the hormone for growth is produced at the tip and travels to the opposite side of the stimulus to cause growth
12
Q
Describe Paal’s experiment to observe phototropism and what it shows
A
- He cut the tip of a coleoptile off and placed it off centre to the plant, in the dark
- The die the coleoptile was placed on grew more than the other side
- This shows that, in the light the phototropic response was caused by a hormone diffusing through the plant tissue and stimulating growth of the tissue
13
Q
Describe Wents experiment to observe phototropism and what it showed
A
- Went placed the cut tip of a coleoptile on a gelatine block, allowing the hormones from the tip to diffuse into the block
- The block was placed on the coleoptile off centre in the dark
- The side the block was placed on grew more than the other side
- This shows same as Paals
14
Q
What is the hormone active in phototropic responses
A
- IAA is an auxin, which is a specific growth factor found in plants
- It is synthesis in the meristems, and then passed down the stem to stimulate elongation growth
- IAA activates proteins in the cell walls, causing them to become more flexible and elongate
15
Q
Describe the phototropic mechanism of plants
A
- Phototropism affect shoots and the tips of stems
- The concentration of IAA present determines the rate of cell elongation, and if it isn’t uniform on both sides of the plant, uneven growth will occur
- When light is uneven, the auxins move to the shaded side and stimulate cell elongation, in order to curve the plant towards the light
16
Q
How do auxins affect geotropism in plants
A
- Shoots show negative geotropism and grow away from gravity, which modifies the auxins to move to the lower side of the shoot, increasing its growth upwards
- Roots show positive geotropism, and the auxins move to the lower side of the root to inhibit cell elongation to lower the growth rate forcing the roots to grow downwards
17
Q
What are the limitations of the practicals for auxin affects on plants
A
- Although species of plant is controlled, each plant has its differences
- Markers to identify growth may be moved
- Eveness of growth can be hard to determine
18
Q
How do plant hormones assist in leaf loss
A
- In hot or dry environments some plants loose their leaves to reduce water loss, or in winter when water absorption is hard to lower photosynthesis demands
- A layer of cells (abscission layer) is developed at the base of leaf stalks, with thin cell walls
- Plant hormone ethene is produced in response to shortening days (in winter) and stimulates the breakdown of these cell walls, causing the leaf to drop
- Auxins also inhibit leaf loss by being produced in young leaves and making young plants insensitive to ethene so they can grow until it’s necessary for abscission to occur
19
Q
How do plant hormones assist in stomatal closure
A
- During water stress, hormone ABA is produced by plants to stimulate the closing of stomata
- Guard cells have ABA receptors on their cell surface, which get bound to by ABA, inhibiting proton pumps and stopping the active transport of H+ ions out of the guard cells
- ABA also causes Ca2+ ions to move into the cytoplasm of guard cells, where they act as secondary messengers causing channel proteins to open and let -ve ions out, as well as K+ ions out of the cell
- This increases the water potential of the guard cells, so water leaves via osmosis, and they become flaccid allowing the stomata to close
20
Q
How do plant hormones assist in seed germination
A
- When a seed is shed from the parent plant it is dormant, allowing it to survive in harsh conditions until the environment is good for growth
- Abscicic acid which keeps the seed dormant must be reduced for germination to start
- When this happens the seed absorbs water to begin germination, which stimulates the embryo to produce gibberellins
- Gibberellin molecules diffuse into the aleurone layer and stimulate cells to synthesis amylase, so amylase in the endosperm produces soluble maltose molecules
- The maltose molecules are converted into glucose and transported to the embryo for respiration and germination to occur
21
Q
Define apical dominance
A
The auxins that are produced at the apex of the plant stem cause the stem to grow upwards and also stop lateral buds from growing
22
Q
Why is apical dominance ideal
A
- Plants need to grow upwards towards the light to ensure the plant has enough energy for photosynthesis
- Sideways growth is less useful so apical dominance caused by auxins ensures growth is upwards
23
Q
Why are lateral buds sometimes useful
A
- If the apex of a plant is removed, lateral buds grow from the top of the plant
- There is no longer apical dominance as the source of auxins have been removed
- With time the lateral shoots curl upward towards the light and the plant grows upwards to gain energy for photosynthesis
24
Q
What is the experimental evidence for the role of gibberellins in stem elongation
A
- Dwarf plant varieties have been shown to have low levels of gibberellins due to a mutation involved in the hormones synthesis
- Under experimental conditions, when gibberellins is administered, the plants grow to the same height as normal varieties
25
Q
What is the experimental evidence for the role of gibberellins in seed germination
A
- Gibberellins stimulating germination and the breaking of dormancy is shown by seeds of mutant varieties of plants that are changed to not produce gibberellins, can be induced to germinate after gibberleins are added
- Seeds of certain lettuce varieties that need light to germinate, can germinate in the dark after gibberellins are administrated
26
Q
Describe the practical process to observe the effect of plant hormones on growth
A
- Make a 5% solution of IBA, and make serial dilutions of it in alcohol
- 10 stem cuttings for each solution should be taken from the same plant, and the ends of them dipped in each solution
- Keep a final 10 cuttings for a control group which are only dipped in alcohol
- After a set time remove the cuttings and roots, and weigh
27
Q
What are the limitations of the practical to measure the effect of plant hormones on growth
A
- Factors need to be controlled, like light intensity, humidity, temperature, and this is difficult to do accurately, so that the concentration of auxins is the only factor in play
- The cuttings must be obtained form the same plant, which can be difficult when lots of cuttings are needed
28
Q
What are ways that plant hormones can be used commercially
A
- As weed killers
- As rooting powders
- To control ripening
29
Q
How are hormones used as selective weed killers
A
- Extremely high concentrations of auxins can cause rapid growth of plants, which distorts and damaged them allowing pathogens into the plant
- Synthetic auxins are used for this process as large concentrations can be applied
- This treatment is effective against weeds that occur in laws or cereal crops as they are less sensitive to the auxins
30
Q
How are hormones used as rooting powders
A
- At low doses auxins can stimulate cuttings to grow new roots, so can be sold in the form of rooting powders
- The end of the cutting is dipped in powder then planted
31
Q
How are hormones used in the control of ripening
A
- Ethene can be used to stimulate fruit to ripen, to reduce fruits being transported whilst ripe and being damages
- Fruits are harvested unripe and ripened artificially with ethene
39
Q
Label diagram of the brain
A
40
Q
What is the structure and function of the cerebrum
A
- Largest part of the brain and is divided into two cerebral hemispheres which are held together by nerve fibres (corpus callosum)
- Consists of 5 lobes, and is surrounded by a thin outer layer (cerebral cortex) beneath which is the ‘white matter’ which consists of myelinated axons of neurones
- The cerebral cortex is highly folded for greater surface area to hold more neurones and increase the ability to carry out functions including vision, hearing, speech, thinking and memory
46
Q
What is the sequence of components in a reflex action
A
- Some receptor cells produce electrical activity whilst others secrete substances
- The coordinator is usually the spinal cord
47
Q
Describe what occurs during the knee-jerk reflex
A
- A ligament in the knee is hit causing the reflex action to occur
- Stimulus: stretching of the quad muscles caused by pressure on the ligament
- Receptor: stretch receptors in the quad muscle
- Impulses are sent from the stretch receptors down the sensory neurones which connect to motor neurones in the coordinator
- Coordinator: spinal cord
- Effector: quad muscle
- Response: contraction of the quad muscle causing the leg to straighten
- No relay neurones present in the knee jerk reflex as the impulse is sent directly from the sensory to the motor neurone
- This causes the reflect to be fast, as the impulse only has to be slowed down at one synapse as opposed to two
48
Q
Describe what occurs during the blinking reflex
A
- Caused by something travelling toward the eye, or contracting the cornea, or drying the cornea
- a irritation of the cornea sends impulses down the trigeminal sensory nerve to the medulla of the brain where it connects with other neurones to transmit a signal to the effector neurones
- Relay neurones transmit impulses to the effectors in the lower eyelid
- Effectors include muscles which contract to close the lower and upper eyelids
50
Q
Describe the mechanism of the fight or flight response
A
- Sensory neurones detect environmental stimuli associated with danger and send impulses to the brain
- The amygdala sends impulses to the hypothalamus, which is stimulate to send impulses via the sympathetic nerves to the adrenal glands
- The adrenal medulla secretes adrenaline, which stimulates its target organs and tissues to increase sensory awareness
- Alongside this the hypothalamus also releases a peptide hormone which stimulates the anterior pituitary gland to release ACTH
- ACTH is transported into the bloodstream, causing the adrenal complex to secrete cortisol which stimulates target organs to increase blood pressure and glucose
52
Q
Describe the second messenger model and how adrenaline works via it
A
- When adrenaline is secreted, it increases the concentration of blood glucose by binding to receptors on the surface of liver cells to activate the same enzyme cascade that happens when glucagon binds to them
- this causes enzyme adenylyl cyclase to change the shape and become activated, allowing it to catalyse the conversion of ATP to cAMP
- cAMP binds to protein kinase A enzymes and activates them, so they can activate phosphorylase kinase enzymes by adding phosphate groups, allowing them to activate glycogen phosphorylase enzymes
- These enzymes catalyse the breakdown of glycogen to glucose, which is known as glycogenesis
- Additionally adrenaline also stimulates the breakdown of glycogen stores in muscles during exercise
55
Q
What are the sections of the autonomic nervous system that controls heart rate
A
- The cardio regulatory centre in the brain is called the medulla, found at the base of the brain near the top of the spine
- The medulla consists of the acceleratory centre, which causes the heart to speed up
- As well as the inhibitory centre which causes the heart to slow down
- Both of the centres are connected to the sinoatrial node by nerves, which makes up the autonomic nervous system
58
Q
How are the acceleratory and inhibitory centres activated
A
- Exercise causes several internal conditions to change creating external stimuli, such as carbon dioxide concentration in the blood, increasing and an initial for in blood pressure caused by dilating arterioles
- These internal stimuli are detected by chemoreceptors and pressure receptors located in the aorta and in the carotid arteries
- These receptors release nerve impulses that are sent to the acceleratory and inhibitory centres
- The frequency of impulses controls the heart rates increased or decrease
64
Q
What is the structure of the sarcolemma
A
- Has many deep tube like projections known as transverse system tubules
- These T tubules run close to the SR
65
Q
What is contained in the sarcoplasm
A
- Mitochondria to carry out aerobic respiration to generate ATP required for muscle contraction
- Myofibrils, are bundles of actin and myosin filaments, which slide past each other during muscle contraction
66
Q
Describe what each part of the myofibril does
A
- Sarcomere is the section of myofibril between two Z lines
- Z line is the attachment for actin filaments
- M line it the attachment for myosin filaments
- I band is where only thin actin filaments are present
- H band is where only thick myosin filaments are present
- A band contains the areas where only myosin filaments are present, as well as where myosin and actin filaments overlap
67
Q
What is smooth muscle
A
- Vital for the unconscious control of many body parts, and contains actin and myosin filaments, but doesn’t have any banding/striation
- Internal organs contain smooth muscle within the walls, e.g. walls of blood vessels
- Smooth muscle consists of small elongated cells/spindle-shaped fibres that contain one nucleus
68
Q
What is cardiac muscle
A
- cardiac muscle is only present within the heart, and is a specialised striated muscle
- It is myogenic, therefore can contract without external stimulation via nerves/hormones
- It doesn’t tire/fatigue so can contract continuously
- Cardiac muscle fibres form a network that spreads through the walls of atria and ventricles, where the muscle fibres are connected to each other via intercalated discs
- Muscle fibres have a large number of mitochondria to produce a large quantity of ATP for continual contraction
69
Q
What does skeletal muscles look like underneath the microscope
A
- Banding/striation is visible
- Banding of myofibrils is visible
70
Q
What do myofibrils look like under the microscope
A
71
Q
Describe how transmission across a neuromuscular junction occurs
A
- Skeletal muscle contracts when it receives an impulse from a motor neuron via the neuromuscular junction (between neurone and muscle cell), which works similarly to the synapse
- when an impulse travels along the axon of a motor neuron and arrive at the presynaptic membrane, the action potential causes Ca2+ ions to diffuse into the neurone
- this stimulates vesicles containing the neurotransmitter acetylcholine to fuse with the presynaptic membrane by binding to receptor proteins on the sarcolemma
- this stimulates ion channels in the sarcolemma to open, allowing Na+ ions to diffuse in, which depolarises the sarcolemma, generating an action potential that passes to the centre of the muscle fibre
- this action potential opens voltage gated calcium ion channel proteins in SR, allowing Ca2+ ions to diffuse into the sarcoplasm
- Ca2+ ions, bind to troponin molecules, causing them to change shape, which triggers the troponins and tropomyosin proteins to change position on the actin, filaments, exposing myosin binding sites to them
76
Q
Describe the process of the sliding filament model
A
- An action potential arrives at the neuromuscular junction where transmission occurs, and myosin binding sites are exposed on the actin molecules
- Globular heads of the myosin molecules bind to the site, forming cross bridges between them, they bend and pull the actin filaments towards the centre of the sarcomere, causing the muscles to contract a small distance
- This is known as the power stroke and it releases a molecule of a ADP
- ATP binds to the myosin head, detaching it from Acton, and the myosin head acts as an ATP is enzyme hydrolysing ATP to ADP, and a phosphorus ion
- The energy released from this action, allows the myosin head to return to its original position, and bind to the new binding site on the actin filaments
- As long as troponin and tropomyosin aren’t blocking the myosin binding sites, and the muscle has a supply of ATP, this process repeats until the muscle is fully contracted
