Plant structures and their functions (6) Flashcards
What are photosynthetic organisms?
The main producers of food and therefore biomass.
What is photosynthesis?
An endothermic reaction that uses light energy to react carbon dioxide and water to produce glucose and oxygen.
How is the structure of a root hair cell adapted to absorb water and mineral ions?
It causes the root to have a large surface area to absorb as much minerals and water as possible. Water is absorbed by osmosis and mineral ions by active transport due to a higher concentration of mineral ions in the root hair cell.
How are the xylem and the phloem adapted to their functions?
Xylem:
Made of dead lignified cells. Xylem tubes transport water and mineral ions from the roots to the leaves. This is the transpiration stream.
Phloem:
Made of living elongated cells. Phloem tubes transport sucrose made in the leaves to other areas of the plant for immediate use or storage. This is called translocation and requires energy from respiration.
How do stomata work?
Stomata are tiny pores on the lower surface of the leaf. They allow diffusion of carbon dioxide in and oxygen out of the leaf. They also allow water vapour to escape during transpiration due to a lower concentration of water outside of the plant. Stomata open when guard cells become turgid and close when they become flaccid.
What is the transpiration stream?
As water diffuses out of stomata, this causes a shortage of water in the leaf causing water to be drawn up from the roots via xylem tubes leading to a constant flow of water and the mineral ions diffused inside of it.
How is the structure of the leaf adapted for photosynthesis and gaseous exchange?
The leaf has a waxy cuticle which reduces water loss by evaporation. The upper epidermis is transparent so light can pass through it to the palisade layer where photosynthesis occurs as there are many chloroplasts. The spongy mesophyll tissue contains many air spaces to increase the rate of gaseous exchange. The lower epidermis contains lots of stomata which are responsible for gaseous exchange. The leaf is also broad to increase surface area exposed to light.
What is the effect of environmental factors on the rate of water uptake?
Light intensity:
The brighter the light the greater the transpiration rate. Stomata begin to close when it is dark as photosynthesis cannot happen in the dark.
Temperature:
The warmer it is the faster transpiration happens because water particles have more energy to evaporate and diffuse quickly.
Air flow:
The better air flow the greater the transpiration rate. If air flow is poor, water vapour accumulates around stomata decreasing the concentration gradient and therefore the rate of transpiration.
How do plant hormones control plant growth?
Growth in shoots:
When a shoot tip is exposed to light, auxins accumulate on the side that’s in shade causing cells on that side to elongate faster making the shoot bend towards the light. This means that shoots are positively phototropic.
This also means that they are negatively gravitropic as gravity causes auxins to accumulate on the bottom of the shoot if it’s growing on its side.
Growth in roots:
A root growing on its side will have more auxins on the bottom side. However, auxins in the roots inhibit growth causing the upper side to grow faster than the bottom and bend downwards. This means that roots are positively gravitropic.
If a root is exposed to light auxins accumulate on the shaded and inhibit growth bending the root to the soil. This means that roots are negatively phototropic.
What are some commercial uses of plant hormones?
Auxins:
Weed killers - most weeds are broad leaved. Selective weed killers that disrupt the growth pattern of broad leaved plants are used to kill them without damaging grass and crops.
Rooting powders - when trying to clone plants, cuttings from the plant are taken and rooting powders containing auxins allow them to grow new plants.
Gibberellins:
Fruit and flower formation - gibberellins stimulate plant germination and so can be used to make plants flower earlier or in conditions they normally would not flower in. They can also be used to reduce flower formation leading to better quality fruit.
Producing seedless fruit - gibberellins are applied to unpollinated flowers creating seedless fruit.
Ethene:
Controlling the ripening of fruits - fruits can be picked while still unripe (less easily damaged) and ethene can be added to ripen them before they arrive at the supermarket.
