Transport and Coordination in plants GCSE

• WP of cytoplasm = WP of solution (out of cell) • No change in cytoplasm So there’s no net osmosis movement due to the net movement of water in and out of the cells being equal - equilibrium

• WP of cytoplasm < WP of solution • Net movement of water into the cell by osmosis • The cytoplasm swells, pushing the cell membrane against the cell wall • Resulting turgor pressure keep the cell rigid or turgid

• WP of cytoplasm > WP of solution • Net movement of water out of the cell by osmosis • The cell becomes plasmolysed - the cytoplasm shrinks and the cell membrane pulls away from the cell wall • The plasmolysed cell becomes floppy or flaccid

• (In a diagram, it is outermost in the vascular bundle) • To transport the products of photosynthesis from the leaves to the rest of the plant. The phloem can move materials up and down the stem. • Sugars for energy, amino acids for building proteins these are normally carried to young leaves and other growing points in the plant. Sugar may be taken to roots to be stored as starch for storage • It is adapted to transport the products of photosynthesis away from the leaves using these adaptations: ○ End walls of phloem are perforated to form sieve plates (the gaps themselves are called sieve pores) ○ Neighbouring cells are connected via cytoplasmic extensions through the holes in the sieve plate ○ Phloem cells have no nucleus to allow the free movement of materials in the cytoplasm ○ They are controlled by neighbouring companion cells (have nucleus that control it), sieve tubes have no nucleus

• (In a diagram, It is the innermost in the vascular bundle) • To transport water and dissolved minerals from the roots to the leaves • Xylem transports water and dissolved minerals from the roots to the leaves • Water and mineral ions are moved in it using the transpiration stream. • Cell walls start alive but as they develop, the become elongated and gradually their original cellulose cell walls become lignified meaning they have lignin. Lignification makes them very strong and enables them to carry water up tall plants without collapsing. Lignin is also impermeable to water. • The substances are transported up inside the lumen of the vessel. • Adaptations for this include: ○ Vessels contain no cytoplasm as they are dead ○ Cross-walls between vertically adjacent cells are broken down to form long continuous vessels ○ Cell walls are strengthened with a woody material called lignin so the stem vessels don’t collapse

• Root hair increases the SA of the root • Water in the soil that surrounds the root hair has a low concentration of solutes (minerals) dissolved in it • Cell sap and cytoplasm have a high concentration of solutes (minerals, sugars, etc) This decreases the WP of the cell so water goes from soil -> cell • Soil water has a higher WP than the cytoplasm so ○ Water moves from the soil into the root hair cell by osmosis ○ Across the partially permeable cell membrane

• Transpiration = loss of water vapour from the leaves of a plant. Water evaporates out of the mesophyll cells and then water vapour diffuses out of the stomata. • Transpiration stream ○ Water and minerals are absorbed by the roots ○ Water is lost from the leaves in a process called transpiration § Water evaporates from the cells into the air spaces in the leaves § Water vapour diffuses out of the leaves via the stomata ○ Transpiration creates a region of low pressure in the leaf, so… ○ The column of water in the xylem tissue is pulled upwards, carrying dissolved minerals in it

• Humidity ○ Shallower concentration gradient as the WP of inside the leaf and outside the leaf is similar. Decreases. • Wind speed ○ Increases concentration gradient as the wind blows away any evaporated water, maintaining the high concentration gradient. Increases. • Light intensity ○ Stomata opens more in light, so more water diffuses out by evaporation. Increases. • Temperature Rate of evaporation is increased so rate of transpiration increases. • Surface area of leaves ○ More SA for evaporation. There are more stomata in the leaf so more water vapour can exit the leaf.

• Set up your potometer • Record the initial position of the meniscus in the capillary tube. • Record the initial position of the meniscus and start the stopwatch. After 1-5 minutes, record the final position of the meniscus and the time. The slower the meniscus is moving, the longer you may wish to leave it. Record the time taken. • Work out the distance moved by the meniscus and the rate. Rate=distance moved by meniscus/total time taken • Repeat the experiment for the different conditions: a. Test under normal room conditions b. Cover with a clear plastic bag - humid c. Test in the air-flow from a hairdryer on cold setting - wind d. Place under a bench lamp and retest - light intensity e. Remove all the leaves but one and retest - surface area of leaves

waste products of metabolism and they both diffuse through the stomata. CO2 is a product of respiration and O2 is a product of photosynthesis.

• Plants respond by growth, not movement • Plants use growth hormones • Plants can grow towards or away from stimuli • e.g. shoots towards light (+ve phototropism) and away from gravity (-ve geotropism), roots away from light and towards gravity • Advantages of shoots to light are increasing the SA of leaves that the sun or light hits, increasing the rate of photosynthesis • Advantages of roots to gravity is that they gain access to more minerals/ions and water. This means they also have a better structural stability with deeper roots

• A stimulus, receptor and effector are used. • A stimulus is any change in the environment • A receptor is a (group of) cell(s) or organ that is sensitive to a stimulus • An effector does an action as a response to the stimulus

stimuli

• Phototropism - growth response to light • Geotropism - growth response to gravity • Shoots grow towards light, positive phototropism, but away from gravity, negative geotropism • Roots grow away from light, negative phototropism, but towards gravity, positive geotropism

• Auxins are chemical messengers which control the responses of plants. They are like plant ‘hormones’ • They are produced in the tips of shoots. The auxins then diffuse through the plant tissues to the rest of the shoot. • In shoots auxins cause cells to elongate and to grow faster. By controlling how fast or slow cells grow on each side of the plant, auxins can cause parts of the plant to grow towards or away from a stimulus. • Auxins are produced at the tip of the shoot. They then diffuse down the shoot and accumulate on the shaded/dark side of the shoot. Auxins stimulate the cells to elongate and to grow faster. The unstimulated cells on the light side of the shoot grow slower. Uneven growth of the cells on either side of the shoot cause it to bend towards the light as it grows. • If the head of a shoot is cut off, auxins cannot be produced so it cannot grow or bend towards light but it can still grow. If the tip is covered, the plant thinks that it is receiving no light and so it grows up as if it were in the darkness • Light breaks down auxin which is why the lit side has less auxin. • In shoots, auxin causes more elongation while in roots it causes less elongation.

• When light is applied, it bends towards the light due to the auxins that build up on the shaded side that divide faster than on the non-shaded side • When on something that rotates, it just grows straight as each side gets an equal amount of light on average so the auxins are evenly distributed • Lightproof box - it grows up rapidly as auxins are produced on all sides of the stem to stimulate growth on all sides. This is done so it can try to reach a light source. Seedlings are tall and etiolated (pale). These have small leaves and weak stems as they are prioritising vertical growth to reach light.