Topic 6 Flashcards
Why must organisms respond to changes in their environment?
- To increase their chances of survival.
- This involves detecting changes, processing information and reacting appropriately.
- any change to internal/external environment is called a stimulus
Define Stimulus
a detectable change in the internal/external environment of an organism e.g. change in temp, light intensity or chemical concentrations
Define Receptor
- specialised cells/proteins on cell surface membranes that detect stimuli, e.g. rods and cones in the retina of eye detect light (photoreceptors) or baroreceptors in blood vessels detect pressure changes
- receptors communicate with effectors via the nervous system or hormonal system or sometimes both
Define Response
a reaction to a stimulus. May involve movement (e.g. escaping a predator) or physiological changes (e.g. secreting a hormone)
Define Effectors
cells that bring about a response to a stimulus, to produce an effect, e.g. muscle cells and cells found in glands
What is Phototropism in plants?
- growth in response to light
-
shoots are positively phototrophic, so grow towards light
roots are negatively phototrophic so grow away from light
What is Gravitropism (geotropism) in plants?
- growth in response to gravity
- shoots are negatively gravitrophic, so grow upwards, against gravity
- roots are positively gravitrophic, so grow downwards with gravity
What are Growth factors in flowering plants?
- in flowering plants, specific growth factors move from growing regions to other tissues, where they regulate growth in response to directional stimuli
- specific growth factors are hormone-like chemicals that slow down or speed up plant growth
- produced in the growing regions of the plant and they move to where theyre needed in other parts of the plant
- growth factors called auxins stimulate the growth of shoots by cell elongation
- high concentrations of auxins inhibit growth in roots
What is Indoleacetic Acid (IAA)?
- an auxin produced in the root and shoot tips of flowering plants
- IAA distribution controls tropisms by influencing cell elongation in response to environmental stimuli
- it moves via active transport and diffusion over short distances and via the phloem over long distances
- the uneven distribution of IAA in response to environmental stimuli creates differential growth rates, leading to tropisms
- IAA encourages cell elongation in shoots, but inhibits cell elongation in roots
How does IAA affect Phototropism in flowering plants?
- IAA moves to the more shaded parts of roots and shoots, so there is uneven growth
- when a shoot is equally illuminated from all sides, IAA is evely distributed, so cells elongate at same rate, casuing stright upwards growth of the flowering plant
- when a shoot is illuminated from one side, IAA moves towards the shaded side of the shoot, so cells on the shaded side elongate faster, casuing the shoot to bend towards the light
- In Roots IAA concentration increases on the shaded side, which inhibits growth, so root bends away from the light
How does IAA affect Gravitropism in flowering plants?
- IAA moves moves to the underside of roots and shoots, so there is uneven growth
- In Roots IAA accumulates on the lower side due to gravity, which inhibits growth, so cells on the upper side elongates faster, and roots bends downwards into the soil
- In Shoots, IAA accumulates on the lower side, promoting growth, so cells on the lower side elongate faster, causing shoot to bend upwards, against gravity
What is a Tactic response (Taxes) in simple organisms?
- organisms move towards or away from a directional stimulus e.g. light
- positive taxes= movement towards a stimulus
- negative taxes= movement away from a stimulus
- e.g. negative phototaxis in woodlice, that move away from light, which helps them survive as it hides them from predators and keeps them in damp conditions, which reduces water loss
What are kinetic responses (Kinesis) in simple organisms?
- random movement of an organism in response to a non directional stimulus e.g. humidity
- e.g. woodlice show a kinetic response to humidity. They move faster in dry environment and change direction more frequently, which increases the chance of finding a damp area.
What are the differences between Taxis and kinesis?
- Taxis involves directional movement and the stimulus determines the direction
- Kinesis involves non directional movement. The stimulus affects the movement rate
What is a Reflex?
- fast, involuntary response to a stimulus, without making a conscious decision to respond.
