5.1.5 - PLANT + ANIMAL RESPONSES Flashcards
What is herbivory?
Plants being eaten by animals (herbivory)
Explain how plants respond to herbivory
Have chemical defences
- Pheromones - chemicals released by a species to affect another organism in the same species (e.g. ETHENE causing ripening of fruit in nearby plants)
^— ETHENE also toxic to insects - Alkaloids - chemicals with bitter tastes, noxious smells or poisonous characteristics that deter/kill herbivores (e.g. tobacco plants produce alkaloid NICOTINE in response to tissue damage)
- Tannins - bitter tasting | can bind to proteins in the gut in some herbivores (e.g. cattle), making the plant hard to digest
What is abiotic stress?
Anything harmful that is natural but non-living
E.g. drought
Explain how plants respond to abiotic stress
Carrots produce antifreeze proteins at low temps
^— proteins bind to ice crystals + lower temperature that water freezes at, stopping more ice crystals from growing
Explains how plants respond to being touched
- If a single leaflet (mini leaf-shaped structure that makes up part of a leaf) of this plant Mimosa pudica is touched, a signal spread through the whole leaf, causing it to quickly fold up
- COULD help protect Mimosa pudica against herbivory in many ways: knocking off small insect feeding on the plant, scaring of animals trying to eat it
What is a tropism?
The response of a plant to a directional stimulus (coming from a particular direction)
What is a positive tropism?
Growth towards the stimulus
What is a negative tropism?
Growth away from the stimulus
List the FIVE types of tropism
- Phototropism
- Geotropism
- Hydrotropism
- Thermotropism
- Thigmotropism
What is phototropism?
Growth of a plant towards the light
- SHOOTS ARE POSITIVELY PHOTOTROPIC (grow towards light)
- ROOTS ARE NEGATIVELY PHOTOTROPIC (grow away from light)
What is geotropism?
Growth of a plant in response to gravity
- SHOOTS ARE NEGATIVELY GEOTROPIC (grow upwards)
- ROOTS ARE POSITIVELY GEOTROPIC (grow downwards)
What is hydrotropism?
Plant growth in response to water
ROOTS ARE POSITIVELY HYDROTROPIC (grow towards water)
What is thermotropism?
Plant growth in response to temperature
What is thigmotropism?
Plant growth in response to contact with an object
What are deciduous plants?
Deciduous plants - plants that lose their leaves in winter
^— losing their leaves helped plants conserve water (lost from leaves) during the cold part of the year when its difficult to absorb water from soil (soil water may be frozen) + there’s less light for photosynthesis
Explain the role of plant hormones in leaf loss in deciduous plants
Leaf loss is triggered by shortening day length in the autumn + controlled by hormones
- Auxins inhibit leaf loss (as leaf gets older, less auxin is produced, leading to leaf loss
- Ethene stimulates leaf loss - produced by ageing leaves (as leaves get older, more ethene is produced)
^— a layer of cells (called abscission layer) develops at the bottom of the leaf stalk (where leaf joins the stem) | layer separated leaf from res of plant + ethene stimulates the cells in the abscission layer to expand, breaking the cell walls + causing the leaf to fall off
Explain the role of plant hormones in seed germination
Explain the role of plant hormones in stomata closure
- Plants need to be able to close their stomata in order to reduce water loss through transpiration
^— done using guard cells (found on either side of a stomata pore) - When guard cells are full of water, they are plump and turgid + the pore is open - when the guard cells lose water they become flaccid, making the pore close
- The plant hormone abscisic acid (ABA) is able to trigger stomata closure
^— binds to receptors on the guard cell membranes - causes specific ion channels to open, allowing calcium ions to enter the cytosine from the vacuole
^— increased conc. of calcium ions in cytosol causes other ion channels to open - these ions channels allow ions (e.g. K ions) to leave the guard cells, raising the water potential of the cells - Water then leaves guard cells by osmosis - guard cells become flaccid + stomata close
What are auxins?
- Produced in the tips of shoots in flowering plants
- Works by stimulating cell elongation
Give an example of an auxin
INDOLEACETIC ACID (IAA)
Outline the role of IAA
- IAA moved around the plant to control tropisms - moves via diffusion + active transport over short distances + via the phloem over long distances
^— Results in different parts of the plants having different amounts of IAA | uneven distribution of IAA means there is uneven growth of the plants
Outline the effect IAA has on phototropism
- IAA moves to the more shaded parts of the shoots + roots so there’s uneven growth
- Cells elongate where IAA is (shaded parts) causing shoot to bend towards the light
- When IAA moves to the shaded side of the roots, growth is inhibited so the roots bends away from the light
Outline the effect IAA has on geotropism
- IAA moves to the underside of shoots + roots so there’s uneven growth
- IAA moves to the shaded side of the shoots, cells elongate so the shoots grows upwards
- IAA moves to the shaded side of the root - growth is inhibited so the root grows downwards
What is apical dominance?
- The shoot tip at the top of a flowering plant is called the apical bud
- Auxins stimulate the growth of the apical bud + inhibit the growth of side shoots from lateral buds
- Prevents side shoots from growing, saving energy + preventing side shoots from the same plant competing with the shoot tip for light
Explain the role of auxins in the control of apical dominance
Because energy isn’t being used to grow side shoots, apical dominance allows a plant in an area where there are loads of other plants to grow tall very vast - past smaller plants to reach sunlight
- If you remove the apical bud then the plant wont produce auxins, so the side shoots will start growing by cell division + cell elongation
- BUT if you replace the tip w/ a source of auxin, side shoots development is inhibited - demonstrates apical dominance is controlled by auxins
- Auxins become less concentrated as they move away from the apical bud to the res of the plant | Is a plant grows very tall, the bottom of the plant will have a low auxin concentration so side shoots will start to grown near the bottom
Explain the role of gibberellin on seed germination
- Seed start as to germinate when it absorbs water, activating the production of gibberellins
^— gibberellins cause enzymes to be released that can breakdown the food stores in the seed so that the embryo plant can use the food to respire + make ATP - Evidence suggest that gibberellins cause this to happen by switching on genes that code for amylases and proteases
^— evidence also indicates that abscisic has an antagonistic effect + that it is the levels of these two hormones that control when a seed germinates
Describe evidence for the role of gibberellins on seed germination
- Experiments have been conducted using mutant plant varieties which do not have the gene that codes from gibberellins —> mutant plant seeds did not germinate but when exposed to an external gibberellins source, they did germinate
- Experiments using gibberellin biosynthesis inhibitors also showed that these plants were unable to make gibberellins + their seeds did not germinate —> when plants were given gibberellins, the seed did germinate
Explain the role of gibberellin on stem elongation
- Gibberellins are a small collection of hormones that help plants grow by stimulating elongation on in the stem
- The higher the concentration of gibberellins, the more elongated the stem
Describe evidence for the role of gibberellins on stem elongation
- Dwarf varieties of plants have very low levels of gibberellins
^— often due to a mutation in a gene involved in the synthesis pathway of gibberellins - Scientists have experimented by treating these dwarf varieties with an external source of gibberellins results in them growing to the same height as non-dwarf varieties
- Horticulturalists + farmers apply gibberellin to shorter plants to stimulate growth
Explain the commercial uses of ethene as a plant hormone
- Used to control ripening in fruits
- Unripe fruit can be picked + transported whilst firm, then sprayed with ethene before it is sold
Explain the commercial uses of auxins
- Used in rooting powder used to encourage growth of new roots from plant cuttings
- Used as weedkiller, sprayed over weeds which then grow too quickly
^— stems give way + die
^— too quickly for resources to handle
Explain the commercial uses of gibberellins
What are the components of the mammalian nervous system?
- Peripheral Nervous System
- Central Nervous System
What are the components of the PNS?
- Receptors
- Sensory neurones
- Motor neurones
What are the components of the CNS?
- Brain
- Spinal cord
These are teh coordination centres
What is the autonomic nervous system?
- Works constantly, subconsciously
- Involved with activities such as digestion, which involves no conscious control
What is the somatic nervous system?
- Consciously controlled
- Voluntary and when one decides to move
^— e.g. choosing to stand up
List the 5 key structures of the human brain
- Cerebrum
- Cerebellum
- Medulla oblongata
- Hypothalamus
- Pituitary gland
Describe the structure of the cerebrum
- Largest part of the brain
- Outer layer known as the cerebral cortex
- Made up of many folds + split into 2 hemispheres
Describe the structure of the cerebellum
- Similar to a mini cauliflower
Describe the structure of the medulla oblongata
- Above the spinal cord
Describe the structure of the pituitary gland
Small, lobed structure known as the master gland
Describe the structure of the pituitary gland
Small, lobed structure known as the master gland
Describe the function of the cerebrum
- Controlling conscious thoughts
- Language
- Intelligence
- Personality
- High-level functions
- Memory
Describe the function of the cerebellum
- Coordinating movements + balance
Describe the function of the medulla oblongata
- Centre of control for unconscious activities
^— e.g. breathing + heart rate
Describe the function of the hypothalamus
- Responsible for homeostasis
^— e.g. thermoregulation + osmoregulation
Describe the function of the pituitary gland
- Secretes many hormones to coordinate several responses
^— e.g. osmoregulation
What is a reflex?
A rapid, automatic response to protect an individual from danger
Explain the process of a reflex arc
- Once the stimulus is detected by the receptor, an impulse is passed along the sensory neurone to a relay neurones
- relay neurones passes the impulse onto a motor neurone which is connected to an effector
^— e.g. if hot object: effector = hand + arm muscles | response = muscles contract to move hand away
Give two examples of a reflex arc
- Knee-jerk reaction
- Blinking
What is the fight or flight response?
When mammals are exposed to a potential threat to survival, a series of autonomic responses are triggered to prepare the organism to either fight to survive or run away
Describe the detection of a potential threat
- The autonomic nervous system detects the potential threat, sending an impulse to the hypothalamus
^— results in more impulses being transmitted along the sympathetic nervous system + adrenal-cortical system - Effectors are the adrenal glands, which will release more adrenaline + noradrenaline
^— the release of hormones triggers the hypothalamus to stimulate the release of adrenocorticotropic hormone (ACTH) from the pituitary gland
Describe the action of adrenaline
If blood glucose is too low, adrenal glands will also secrete adrenaline
Describe how adrenaline will increase blood glucose by
- Adrenaline (first messenger) attaches to receptors on target cell surfaces, causing a protein (G protein) to be activated + adenylyl cyclase to convert ATP into cAMP (second messenger)
- cAMP activates an enzyme that can hydrolyse glycogen into glucose
^— KNOWN AS second messenger model of adrenaline + glucagon,
Describe how the endocrine + nervous systems can affect the heart rate
- Heart has inbuilt pacemaker (SAN) + is myogenic
^— BUT can be affected by endocrine + nervous system to respond to stimuli
What effects does adrenaline have on the heart?
- Increases heart rate
- Increases stroke volume
- Increases cardiac output
How does the brain control heart rate?
- Cardiovascular center in the medulla oblongata in the brain controls heart rate via autonomic nervous system
- Heart + medulla oblongata connected via two nerves:
^— accelerator nerve
^— vagus nerve
Describe the role of the accelerator nerve
- Impulses sent via accelerator nerve in sympathetic nervous system INCREASE HEART RATE
Describe the role of the vagus nerve
- Impulses sent via vagus nerve in parasympathetic nervous system DECREASE HEART RATE
Describe how heart rate changes in response to pH
- Detected by chemoreceptors
- pH of blood decreases during time of high respiratory rate due to production of carbon dioxide or lactic acid
- Excess acid must be removed from the blood rapidly to prevent enzymes denaturing
^— achieved by increasing heart rate (more impulses via sympathetic nervous system to SAN) so carbon dioxide can diffuse out into the alveoli more rapidly
Describe how heart rate changes in response to pressure
- If bp is too high this can cause damage to the walls of the arteries + it is important to put mechanisms in place to reduce bp
^— results in more impulses via parasympathetic nervous system to decrease heart rate - If bp is too low, there may be insufficient supply of oxygenated blood to respiring cells + removal of waste
^— results in more impulses via sympathetic nervous system to increase heart rate
What are the three types of muscle fibres?
- Skeletal muscles
- Cardiac muscles
- Involuntary (smooth) muscles)
Describe the structure of skeletal muscles
- Most muscle is skeletal - attached to the skeleton + responsible for causing movement of the skeleton
- Made out of cylindrical shaped cells, which join to form multinucleated myofibrils
- Striated patter when stained + viewed using a microscope
Describe the structure of cardiac muscles
- Heart contains cardiac muscles _ used to pump blood
- Myogenic
- Cells are branched to allow contraction across the whole of the atrium or ventricles + cells are uninucleated
- Striated pattern when stained + viewed using a microscope
Describe the structure of involuntary (smooth) muscles
- Muscle lining organs + blood vessels
- By contracting + relaxing, causes movement of the contents of an organ/blood vessel
^— e.g. controlling diameter or arteries, arterioles, bronchi + bronchioles, pupil dilation - Uninucleated, spindle shaped + unscripted when stained + viewed using a microscope
What is the neuromuscular junction?
- A synapse that occurs between a motor neurone and a muscle fibre
^— very similar to synaptic junction
Describe the characteristics of the neuromuscular junction
- Only excitatory
- Connects motor neurones to muscles
- End point for action potential
- Acetylcholine binds to receptors on muscle fibre membranes
Describe the characteristics of the cholinergic synapse
- Excitatory or inhibitory
- Connect two neurones, which could be sensory relay or motor
- New action potential is generation in the next neurone
- Acetycholine binds to receptors on post-synaptic membrane of a neurones
Describe the role of the neuromuscular junction
- When an impulse arrives at teh end of a motor neurones a neurotransmitter passes across the neuromuscular junction + binds to receptors on the sarcolemma
^— causes the receptors to open, sodium ions move in + the membrane becomes depolarised - Wave of depolarisation is passed down t-tubules causing the sarcoplasmic reticulum to release calcium ions, leading to muscular contraction
What are agonist muscle pairs?
What are antagonist muscle pairs?
Briefly state how muscles move against the bone
- Muscle act in antagonistic pairs against an incompressible skeleton to create movement
- This can be automatic as part of a reflex or controlled by conscious thought
What are myofibrils?
Made up of fused cells that share nuclei + cytoplasm (sarcoplasm) and there is a high number of mitochondria
Describe the structure of the sarcomere
- Muscle fibres made up of millions of myofibrils
- Myofibrils made up of two proteins: myosin + actin
^— which form a sarcomere
Describe how muscles contract in terms of the sliding filament model
- During muscle contraction sarcomeres within myofibrils shorten as the actin and myosin filaments move past each other
^— sliding filament model of muscle contraction - An action potential arrives at the neuromuscular junction + calcium ions released from the sarcoplasmic reticulum into the sarcoplasm by diffusion
- Calcium ions bind to troponin molecules, stimulating them to change shape
^— causes troponin and tropomyosin proteins to change position on the actin filaments - Myosin binding sites are exposed on the actin molecules
- The globular heads of the myosin molecules bind with these sites, forming cross-bridges between the two types of filament
- The myosin heads bend and pull the actin filaments towards the centre of the sarcomere, causing the muscle to contract a very small distance
^— movement of myosin heads known as the power-stroke - When the myosin heads bend, releases ADP molecule
- ATP binds to myosin head, allowing it to detach from actin
- The myosin head acts as an ATPase enzyme, hydrolysing ATP into ADP and Pi; energy released during this reaction allows the myosin head to return to its original position
- The myosin head can now bind to a new binding site on the actin filaments
- The myosin heads move again, pulling the actin filaments even closer to the centre of the sarcomere and causing the sarcomere to shorten further
- As long as troponin and tropomyosin are not blocking the myosin-binding sites and the muscle has a supply of ATP, this process repeats until the muscle is fully contracted
