5.5- Plant and animal responses

Abiotic stresses that plants respond to

Daylength, falling temperatures, water availability

How plants respond to changes in day length

Deciduous plants lose leaves, enter dormancy

How plants know when to respond to changes in day length

The ratio of Pr and Pfr (Forms of phytochrome)

What are Pr and Pfr examples of?

Phytochromes

Photoperiodism

Sensitivity to lack of light in the environment

Plant responses that are affected by photoperiodism

Breaking dormancy of leaf buds, timing of plant flowering, when tubers are formed

Why do deciduous plants do leaf abscission?

The temperature is so low that the amount of glucose required for respiration in the leaves and to produce chemicals to prevent freezing is greater than the amount produced by photosynthesis

How do plants do leaf abscission?

Falling light levels decrease the concentration of auxin, more ethene produced, ethene initiates the switching on of genes in the abscission zone to produce enzymes such as cellulase, cellulase digests the cell wall in the separation zone, vascular bundles sealed off, fatty material deposited into cells in protective layer which forms scar, cells in separation zone retain water, increases strain on separation zone, strain is too much, leaf falls

How do plants respond to lower temperatures?

Cytoplasm and sap of plant cells contain solutes to lower freezing point

How do plants respond to lower water availability?

Roots provide early warning system by producing ABA when there is less water, ABA transported to leaves, binds to receptors on plasma membrane of guard cells, causes changes in ionic concentration of guard cells, reduces water potential of cells, guard cells lose turgor, stomata close

Type of plant responses to herbivory

Physical, chemical, pheromones, folding in response to touch

Physical plant responses to herbivory

Thorns, barbs, spikes, spiny leaves, fibrous tissue, inedible tissue, hairy leaves, stings

Chemical plant responses to herbivory

Tannins, alkaloids, terpenoids

How do tannins protect plants against herbivory?

Bitter tasting, toxic to insects

Why are tannins toxic to insects?

Bind to digestive enzymes and inactivate them

How do alkaloids protect plants against herbivory?

Bitter tasting, affecting metabolism of animals

Examples of alkaloids protecting plants against herbivory

Caffeine produced by coffee bush seedlings is toxic to fungi and insects, caffeine prevents germination of seeds of other plants, nicotine produced by tobacco plants is a toxin stored in vacuoles

How do terpenoids protect plants against herbivory?

Toxins to insects and fungi

Examples of terpenoids protecting plants against herbivory

Pyrethrin from chrysanthemums is an insect neurotoxin, citronella from lemon grass is an insect repellent

Pheromone

Chemical made by an organism which affects the social behaviour of other members of the same species

Examples of pheromones being used to protect plants against herbivory

Maple trees attacked by insects release a pheromone which is absorbed by leaves on other branches which can then prepare

Plant version of pheromones

Volatile organic compounds

How VOCs work

Made when plant defences detected chemicals in insect saliva, elicit gene switching

Examples of VOCs protecting plants against herbivory

Cabbages can produce a signal which attracts parasitic wasps which eats the caterpillar eggs, signal deters other butterflies from laying their eggs, apple trees do the same things, wheat seedlings produce signals that repel aphids when attacked

Example of a plant that folds in response to touch

Mimosa pudica

How do Mimosa podia fold in response to touch?

Touch initiates an action potential, spreads to the base of each petiole, pulvinus is at the base of each petiole, action potential causes K+ and Cl- ions to leave the extensor side of the pulvinus and move into the flexor side, opens voltage gated channels, water leaves the extensor side by osmosis, cells become flaccid on the extensor side and turgid on the flexor side, pulvinus can't support weight of the leaf, leaf droops

Examples of plant tropisms

Phototropism, geotropism, thigmotropism, chemotropism

Tropism

A directional growth response

Phototropism

Response to light

Geotropism

Response to gravity

Chemotropism

Response to chemicals

Thigmotropism

Response to touch

How phototropism works

Light causes the auxin to move laterally across the shoot, greater concentration on unilluminated side, stimulates cell elongation and growth on the dark side

Practical investigations into phototropism

Grow seedlings in different light conditions and use time-lapse photography to observe the changes, grow in unilateral light with different colour filters to see which wavelengths result in the greatest response,

Which kind of organisms are used to study tropisms?

Germinating seeds and young seedlings of monocotyledonous

Why are germinating seeds and young seedlings used to study tropisms?

Easy to work with, changes affect the whole organism, seedlings of monocotyledonous have a single spike with no leaves known as a coleoptile

Practical investigations into geotropisms

Place a plant in a clinostat which is rotating and the plant will grow straight, seeds placed in petri dishes stuck to walls of lab and roots show geotropism

How hormones are involved in seed germination

Seeds absorb water, embryo activated, gibberellins produce, production of enzymes to break down food stores stimulated, food stores used to make ATP, ABA is antagonistic to gibberellins

How do gibberellins stimulate the production of enzymes?

Switch on genes for amylases and proteases

Where are the food stores in dicot seeds?

Cotyledon

Where are the food stores in monocot seeds?

Endosperm

Role of auxins

Stimulate the growth of the main apical shoot, apical dominance, low concentration of auxins promote root growth

How do auxins stimulate the growth of the main apical shoot?

Auxin binds to specific receptor sites in the plant cell membrane, pH falls to 5, optimum pH for enzymes to keep walls flexible and plastic

How auxin does apical dominance?

Growth in the main shoot is stimulated by auxin produced at the tip so it grows quickly, lateral shoots inhibited by the hormone that moves back down the stem, further down the stem there is less auxin so the shoots grow more

Practical investigations into apical dominance

Apical shoot removed, lateral shoots grow faster, the application of artificial auxin to the cut apical shoot reasserts apical dominance

How do gibberellins cause stem elongation?

Affect the length of the internodes

Practical investigations into how gibberellins result in stem elongation

Plants infected by the fungus that produces gibberellins grow tall and thin, plants with short stems produce few or no gibberellins

Experimental evidence into how gibberellins affect seed germination

Mutant varieties which lack the gene that allows them to make gibberellins make seeds that don't germinate, gibberellins applied to the seeds cause them to germinate normally, gibberellin inhibitors cause the seeds to not germinate

How to investigate the effect of hormones on plant growth

Grow seeds hydroponically in serial dilutions of different hormones, apply different concentration to the cut ends of stems

What can plant hormones be used for commercially?

Controlling ripening, rooting powders, hormonal weed killers

How hormones are used to control ripening

Fruits can be harvested when they aren't ripe, greengrocers then spray them with ethene to cause them to ripen

How hormones are used in rooting powders

Auxin applied to cut shoots of cuttings to stimulate root production, increases chances of successful propagation

How hormones are used in hormonal weedkillers

Synthetic auxins can be used as weedkillers as they are absorbed by broad-leaved weeds, causing their growth rate to become unsustainable so they die

How is the mammalian nervous system organised structurally?

Central nervous and peripheral nervous systems

Central Nervous System

Brain and spinal cord

Peripheral nervous system

The neurones that connect the CNS to the body,

How is the mammalian nervous system organised functionally?

Somatic and autonomic nervous systems

Somatic nervous system

System under conscious control, carries impulses to the muscles

Autonomic nervous system

System under subconscious control, carries impulses to glands and smooth muscle and cardiac muscle

How is the autonomic nervous system organised?

Sympathetic and parasympathetic nervous systems

Gross structure of the brain

Protected by the skull, surrounded by meninges, five main areas

Main areas of the brain

Cerebrum, cerebellum, medulla oblongata, hypothalamus, pituitary gland

Functions of the cerebrum

To receive sensory information and interpret it with respect to previous experiences, to send impulses along motor neurones to act on the information, used to control both voluntary and involuntary responses

Structure of the cerebrum

Highly convoluted, split into two halves, has discrete areas for different functions, outer layer called cerebral cortex

How the cerebrum responds to sensory information

Sensory areas receive information from receptor cells in sense organs, information passed to association areas, impulses go into motor areas so impulses can be sent through motor neurones to move muscles

How is the brain able to judge distance and perspective?

Impulses from right side of the field of vision sent to left hemisphere, impulses from left side sent to right hemisphere, integration gives distance and perspective

Function of the cerebellum

To control muscle movement, body posture and balance.

How does the cerebellum work?

Receives information from balance organs, relays information to areas of the cerebral cortex

Function of the medulla oblongata

To control reflex activities as part of the autonomic nervous system, such as ventilation and heart rate

Function of the hypothalamus

Main controlling region for the autonomic nervous system, one centre for parasympathetic system, one centre for sympathetic system, controls complex behaviour patterns, monitors composition of blood plasma, produces hormones

Function of the pituitary gland

To control most of the glands in the body

Structure of the pituitary gland

Divided into anterior and posterior pituitary gland

Function of anterior pituitary gland

To produce hormones such as FSH

Function of posterior pituitary gland

To store and release hormones made by the hypothalamus such as ADH

Reflex arc

Receptor detects stimulus, creates action potential for sensory neurone, sensory neurone carries impulse to motor neurone within the spinal cord via a relay neurone, motor neurone carries impulse to effector

What type of reflex is the knee jerk reflex?

Spinal reflex

Spinal reflex

When the neural circuit only goes up to the spinal cord, not the brain

How does the knee jerk reflex work?

Leg tapped just below the patella, stretches the patellar tendon, initiates the reflex arc, extensor muscle on top of the thigh contracts, relay neurone inhibits motor neurone of the flexor muscle so it relaxes, contraction of the extensor muscle causes the leg to kick

What is the knee jerk reflex used for?

Maintaining posture and balance

Examples of reflex actions

Knee jerk, blinking

What type of reflex is the blinking reflex?

Cranial reflex

Optical reflex

Blinking as a reaction to overly bright light

Cranial reflex

A reflex that occurs in the brain

How does the blinking reflex work?

Irritation of the cornea triggers an impulse along the fifth cranial nerve, passes through a relay neurone in the lower brain stem, impulses then sent along branches of the seventh cranial nerve, results in the eyelids closing

Consensual response

Both things respond in the same way to a stimulus

Example of a consensual response

Blinking reflex

How do reflexes increase your chances of survival?

Involuntary responses so the brain can deal with more complex responses, not learnt so provide immediate protection, fast

Stressor

Stimulus that causes the stress response which causes wear and tear on the body's physical or mental resources

Fight or flight response

Full range of coordinated responses of animals to situations of perceived danger

What is the cause of the fight or flight response?

Shift in the balance of stimulation to increase activity of the sympathetic nervous system and a decrease in activity of the parasympathetic nervous system

How is the fight or flight response coordinated?

Hypothalamus activates sympathetic nervous system and the adrenal-cortical system by releasing CRF, sympathetic nervous system activates the adrenal medulla which releases adrenaline and noradrenaline, sympathetic nervous system leads to impulses that activate glands and smooth muscles, anterior pituitary gland releases ACTH which leads to the adrenal cortex which releases hormones

Hormones that are released by the adrenal cortex in the fight-or-flight response

Cortisol, corticosterone

Role of cortisol

To regulate metabolism and blood pressure responses to stress

Role of corticosterone

Regulates immune response and suppresses inflammatory reactions

How does adrenaline use cell signalling?

Binds to its receptor, activates inactive adenyl cyclase to make active adenyl cyclase which is an enzyme, ATP is then converted into cAMP, cAMP is the second messenger

How is the nervous system involved in increasing heart rate?

Centre in the medulla oblongata which increases heart rate sends impulses through the sympathetic nervous system in the accelerator nerve to the SAN

How is the nervous system involved in decreasing heart rate?

Centre in the medulla oblongata which decreases heart rate sends impulses through the parasympathetic nervous system in the vagus nerve to the SAN

Types of receptors involved in changing heart rate

Chemoreceptors, baroreceptors

How are chemoreceptors involved in increasing heart rate?

Decreases in blood pH are detected due to increased CO2 concentration so heart rate increases to get CO2 to the lungs faster

How are chemoreceptors involved in decreasing heart rate?

pH of the blood rises, detected by receptors in wall of the carotid arteries and aorta, reduction in frequency of impulses sent to the medulla oblongata, reduces frequency of impulses sent to the SAN