3.6.1.1 Survival and response (A-level only) Flashcards
Growth factor definition
-chemicals similar to hormones that speed up or slow down plant growth
Growth factor location
Plants produce growth factors from growing regions/Shoot/Tip
Growth factor function
Growth factors = chemicals similar to hormones that speed up or slow down plant growth.
- Growth factors produced in the growing regions of the plant (shoot tip / leaves) and move to where they’re needed in other parts of the plant.
- Growth factors called auxins stimulate growth of shoots by cell elongation —> where cell walls become loose and stretchy so cells get longer.
- High [auxin] inhibit growth in roots.
Growth factors vs hormones
- they affect growth of the whole part of a plant
- they are not secreted by glands and do not travel in a transport system
- they can sometimes affect the tissues that release them
Auxin definition
-a growth factor that regulates plant growth
Auxin location
-they are produced in the stem, buds, and root tips
Auxin function
- diffuse backwards to stimulate the cells just behind the tip to elongate( walls become lose and stretchy) so the cell gets longer.
- Stimulate growth by cell elongation
Auxin examples
-IAA, controls directional growth seen in tropism in flowering plants
IAA definition
- indoleacetic acid
- an important auxin
- produced in the tips and shoots of flowering plants
IAA location
produced by the meristem cells
- produced in the tips and shoots of flowering plants
IAA function
- diffuse backwards to stimulate the cells just behind the tip to elongate( walls become lose and stretchy) so the cell gets longer.
- Stimulate growth by cell elongation
IAA movement around plant
- diffusion and active transport over short distances
- via the phloem for longer distances.
Tropism definition
the growth of part of a plant in response to a directional stimulus e.g. light, gravity, water
Tropism types
- positive gravitropism
- negative gravitropism
- positive phototropism
- negative phototropism
gravitropism definition
-Gravitropism is the growth of a plant in response to gravity.
Gravitropism process
- IAA moves to the underside of shoots and roots so there is uneven growth.
Positive gravitropism definition
The downwards growth of a plant towards gravity
Positive gravitropism process
- IAA concentration increases on the lower side, growth is inhibited so the roots grow downwards.(ROOT)
Positive gravitropism survival advantage
anchors the plant into the soil and increases chances of absorbing water & ions
Positive gravitropism example
- Roots are positively gravitropic and grow downwards towards gravity
Negative gravitropism definition
The upwards growth of a plant away from gravity
Negative gravitropism process
- IAA concentration increases on the lower side, cells elongate so the shoot grows upwards.(SHOOT)
Negative gravitropism survival advantage
Shoots- grow out of soil , leaves exposed to sun
Negative gravitropism example
Shoots are negatively gravitropic as they grow upwards away from gravity
phototropism definition
- Is the growth of a plant in response to light
Positive phototropism definition
-the growth of an organism towards the source of light
Positive phototropism process
- IAA is produced by cells in the top of the shoot and is then transported down the growing region where growth is stimulated by causing more cell elongation to occur
- the IAA is transported evenly when it begins to move down the shoot
- light from one side causes the movement of IAA from the light side to the shaded side of the shoot
- a higher concentration of IAA builds up on the shaded side, causing more elongation of the cells than on the light side
- the shaded side grows at a faster rate than the illuminated side, causing the shoot to bend and grow towards the light
Positive phototropism survival advantage
can absorb light so more photosynthesis (LDR) so more carbohydrate produced for growth
Positive phototropism example
- Shoots are positively phototropic and grow towards the light.
Negative phototropism definition
-the growth of an organism away from the source of light
Negative phototropism process
IAA INHIBITS Cell elongation
1) cells in ROOT TIP produce IAA
2) diffuses down to root tissue to SHADED side
3) to inhibit shaded cell elongation, bend away from light
Negative phototropism survival advantage
anchors the plant into the soil and increases chances of absorbing water & ions
Negative phototropism example
- Roots are negatively phototropic and grow away from the light.
Reflex definition
Rapid, innate, unlearned response to a stimulus.
—> so quick as information can travel rapidly from receptors to effectors - no need to think.
Reflex characteristics
so quick as information can travel rapidly from receptors to effectors - no need to think.
-involuntaury: - The pathway of communication goes through the spinal cord but not the conscious part of the brain, so the response is automatic.
Reflex survival value/ advantage
help organisms to avoid damage to their body because they provide a rapid response
Advantage of simple reflexes
- Rapid;
└ as they involve fast electrical impulses and very short neurone pathways - Protect against damage to body tissues;
- Do not have to be learnt;
- Help escape from predators;
- Enable homeostatic control;
-involuntary
└ don’t involve decision-making areas of the brain, leaving them free to carry out more complex responses
Reflex arc definition
- The pathway of neurones linking receptors to effectors in a simple reflex is called a reflex arc.
- These neurones are involved a sensory neurone, a relay neurone and a motor neurone.
Reflex arc example- response to heat
- reflex arc.
Reflex arc = the pathway of neurones linking receptors to effectors in a reflex.
1. Thermoreceptors in the skin detect the heat stimulus.
2. Sensory neurone carries impulses to the relay neurone.
3. Relay neurone connects to the motor neurone.
4. Motor neurone sends impulses to the effector (biceps muscle).
5. Muscle contracts to withdraw hand and stop it being damaged.
NB => If there is a relay neurone involved in the simple reflex arc, it is possible to override the reflex.
Stimulus definition
A detectable change in the internal or external environment of an organism that produces a response
Receptor definition
a protein molecule that receives chemical signals from outside a cell
Sensory neurone
Receptor → CNS
relay neurone
CNS→CNS
motor neurone
CNS→effector
effector definition
Responds to stimulus
e.g. muscle, gand
response definition
any behavior of a living organism that results from an external or internal stimulus.
Simple responses definition
Taxes and kineses are simple responses that can maintain a mobile organism in a favourable environment
Simple responses characteristics
- they are genetically determined, and cannot be adapted or modified to suit changing circumstances
- they show a stereotyped pattern, similar in all members of that species, although some differences may exist between the males and females
- the behaviour often consists of a chain of reflexes in which each link in the chain provides the stimulus for the commencement of the next
- they are typical of simple organisms with a short life cycle, where learning has little opportunity to occur
Simple responses examples
Taxis
Kinesis
Taxis definition
A simple, directional response to a stimulus, and is carried out by the whole organism. The direction of the stimulus determines the direction of the response
Taxis types
Positive taxis
Negative taxis
Positive taxis
Movement towards a stimulus by a whole organism.
Negative taxis
Movement away form a stimulus by a whole organism.
Taxis examples + survival value
Positive phototaxis: single-celled algae/protoctista move towards light as needs light for photosynthesis to produce organic compounds. Increases survival chances
Negative phototaxis- earthworms that move away from light as better able to conserve water (avoid dehydration) find food & avoids predators
Kinesis definition
Random movement of a whole organism in response to a non-directional stimuli e.g. temp or humidity. This may be an increase/decrease in speed or turning frequency.
Kinesis examples + survival value
Woodlice
- non-directional response to humidity
- In dry air - woodlice move faster & turn less often to increase their chance of moving away from drier air. This will increase their survival chances by reducing water loss. Also humidity higher in concealed places so safe from predators.
- as air becomes more humid they move slower & turn more often so they are more likely to stay in that area
