Term 2b Flashcards
(18 cards)
What is diffusion?
The movement of molecules from a region of higher concentration to a region of lower concentration
Diffusion in living organisms
Molecules move into or out of living cells by diffusion when they cross the cell membrane
The cell membrane is partially permeable, meaning that it allows some molecules to cross, but not others
E.g. smaller molecules can diffuse across the membrane but larger molecules cannot
Diffusion allows living organisms to?
gain nutrients in the digestive system
gain oxygen in the lungs
remove waste products in the lungs and kidneys
What is active transport?
The movement of particles across a cell membrane from a region of lower concentration to a region of higher concentration
Multicellular Organism what is it?
an organism that is made of many cells, such as plants, animals or fungi
What does multicellular organism need transport systems ?
These organisms have multiple cell layers, making the distance from the surface to the centre too long for diffusion alone
Diffusion to all cells would be too slow to meet the organism’s needs, so larger organisms require transport systems
What makes up the transport system in vascular plants?
Xylem and phloem
What is the role of xylem?
The role of the xylem is to transport water and mineral ions from the roots to other parts of the plant
The xylem is formed from a hollow tube of dead cells, reinforced by lignin, which provides a route for the column of water to move through the plant by transpiration.
What is the role of phloem?
The role of the phloem is to transport sucrose and amino acids from where they are produced or stored, to where they are needed
E.g. sucrose and amino acids are produced in the leaves while plants photosynthesise, so they are transported from the leaves to other parts of the plant
The phloem is formed from living cells forming a tube with small holes through which substances can move.
Response to stimuli and examples?
Plants need to be able to grow in response to certain stimuli
For example, plants need to be able to grow in response to light, to ensure their leaves can absorb light for photosynthesis
They also need to be able to grow in response to gravity, to ensure that shoots grow upwards and roots grow downwards
The directional growth responses made by plants in response to light and gravity are known as tropisms
If the growth is towards the stimulus, the tropism is positive and if the growth is away from the stimulus, the tropism is negative
What is geotropic response to plants?
a response to gravity is a geotropism
What is a response to phototropism?
A response to light is a phototropism a
Phototropism positive and negative response?
Positive response:Growth towards the light source
Negative response: Growth away form the light
Geotropism positive and negative response?
Positive response: Growth towards the source of gravity
Negative opposite
The role of auxin in Phototropism?
Plants produce plant growth regulators (similar to hormones in animals) called auxins to coordinate and control directional growth responses such as phototropisms and geotropism
Comparison of Photo and geo?
As shoots grow upwards, away from gravity and towards light (so that leaves are able to absorb sunlight), shoots show a positive phototropic response and a negative geotropic response
As roots grow downwards into the soil, away from light and towards gravity (in order to anchor the plant and absorb water and minerals from the soil), roots show a negative phototropic response and a positive geotropic response
Where is auxins located in a plant?
Auxin is mostly made in the tips of growing shoots and then diffuses down to the region where cell division occurs (just below the tip)
This is an important point - only the region behind the tip of a shoot is able to contribute to growth by cell division and cell elongation
How does the auxin change when the direction of the light changes?
Auxin stimulates the cells in this region to elongate (get larger); the more auxin there is, the faster they will elongate and grow
If light shines all around the tip, auxin is distributed evenly throughout and the cells in the shoot grow at the same rate - this is what normally happens with plants growing outside
When light shines on the shoot predominantly from one side, the auxin produced in the tip concentrates on the shaded side, making the cells on that side elongate and grow faster than the cells on the sunny side
This unequal growth on either side of the shoot causes the shoot to bend and grow in the direction of the light
