Plant Structures And Functions Flashcards
What is photosynthesis?
An endothermic reaction(takes in light from the sun) which occurs in the chloroplasts
-6carbon dioxide + 6water — (light)— glucose + 6oxygen
How can we tests a lead to identify the presence of starch?
- boil the leaf in water to make it floppy do it can fit in the test tube
- place in ethanol to remove the chlorophyll to de colourised it
- add iodine and where starch is present the will turn blue/black
What is the law of limiting factors?
When a process depends on two or more factors, the rate if the process is limited by the factor which is in shortest supply
How does carbon dioxide effect the rate of photosynthesis?
As carbon dioxide increases so does the rate of photosynthesis until it reaches a maximum rate. It increases because CO2 is a raw material needed in photosynthesis. The rate increase until another factor begins to limit it
What effect does light have on the rate of photosynthesis?
Light transfers the energy needed for photosynthesis. As light level is raised, the rate if photosynthesis increases steadily but only up to a certain point until another factor starts to limit it.
How does temperature effect the rate of photosynthesis?
As temperature increases, the rate increases until it reaches the optimum temperature and then it decreases again.
-temperature increases the rate of chemical reactions as particles have more Kenergy. When optimum temp passes the enzymes denature so the rate decreases
What adaptations and processes do root hair cells partake in?
- root hair cells have hairs to provide a large surface area, many mitochondria and a thin cell wall
- minerals are absorbed by active transport into the cell as there is usually a higher concentration
- water is absorbed through diffusion as there is usually a higher concentration of water in the soil
What is transpiration?
The loss of water from plants which tends to happen in the leaves
What is the xylem?
Xylem tubes are made from dead cells joined together and strengthen by lignin so the walls don’t collapse. There are no end walls to impede water flow and has a hole down the middle
They carry water and mineral ions from the roots to the stem and leaves
How does transpiration work?
- water passes into the lead by osmosis to replace the water which has been lost
- water containing mineral ions is pulled upwards through xylem vessels as they contain a continuous column of water due to weak forces of attraction between water molecules
- water evaporates from the stomata
What is a potometer?
Can estimate the rate if transpiration but is only an estimate as it measures water uptake but some is used in photosynthesis
What is a stomata?
Stomata only open if there is enough water in the guard cell and are used for gas exchange. When the stomata opens to let CO2 in and looses water through diffusion.
-most stomata are underneath the leaf to limit evaporation
How does light effect the rate of transpiration?
In bright light transpiration increase as more light means more photosynthesis. This means the stomata opens more to allow CO2 in so more water is lost
How does temperature effect the rate if transpiration?
Transpiration is faster in hotter temperatures as evaporation and diffusion take place at a faster rate as they have more energy. Warm air is also able to absorb more water vapour than cool air.
How does humidity effect rate of transpiration?
Transpiration is slower in humid conditions as diffusion slows down as the air is already saturated with water molecules. This creates a lower concentration gradient
How does wind effect the rate of transpiration?
Transpiration is faster in windy conditions as saturated air with water vapour is removed quickly by air creating drier are to speed up diffusion
What is a positive outcome of transpiration?
It cools the plant as water evaporates
How does a thicker waxy cuticle of a xerophyte reduce transpiration and help it survive?
Reduces water loss through epidermis as it is hydrophobic. This means less evaporation and so less transpiration
How does small leaves/needles of a xerophyte reduce transpiration and help it survive?
Deciduous plants loose leaves during winter when they may not be able to photosynthesis. This means there is a smaller surface area and fewer stomata so there is less evaporation and transpiration
How does sunken stomata (pits) of a xerophyte reduce transpiration and help it survive?
Stomata on the underside of the leaf to reduce direct heating and transpiration
-hairs trap water vapour which stops the wind removing it. Thus there is more water particles around the leaf(humid air)which reduces the concentration gradient and therefore transpiration
How does a stomata shutting in the night and opening in the day of a xerophyte reduce transpiration and help it survive?
Stomata closes at night so there is no light for photosynthesis so no water is lost
It is also warmer in the day so there is more evaporation
How are leaves adapted to benefit gas exchange in photosynthesis?
- leaves are broad so a large surface area is exposed to light
- the palisade layer has a lot of chloroplasts
- the epidermal tissues are covered with a waxy cuticle which helps reduce water loss by evaporation
What is translocation and the role of phloem?
Plants make sucrose from the glucose which is made in photosynthesis-this is translocated in the phloem vessels and is transported to all parts of the plant
What are the first 3 stages of translocation?
- starch is made by photosynthesis in chloroplasts
- starch is broken down when it is dark and the products of the breakdown are moved into the cytoplasm of the cell
- starch is used to make sucrose which is a Soluble sugar
What are stages 4 and 5 and 6 of translocation?
- sucrose is moved by active transport into companion cells
- companion cells pump sucrose into sieve cells
- the sieve and companion cells form phloem. The pumping of sucrose into the sieve cells causes a pressure difference causing the content of the sieve cell to move up or down
What are the adaptations of companion cells and sieve cells?
- Companion cells have many mitochondria to release energy and have small pores between them and sieve cells
- sieve cells have no nucleus and only small cytoplasm in order to make the central channel wider to make the flow of liquids easier
What is a tropism?
Responding to a stimulus by growing away or towards it (e.g. light, gravity and water)
What are auxins?
Auxins are plant hormones which inhabit growth in the roots and stimulate growth in the shoots of plants - they are found in the meristem
What is positive and negative tropism?
Positive tropism is going towards the stimulus
Negative tropism is going away from the stimulus
What is the stimulus for the tropism needed to know?
- phototropism = sun
- gravitropism = gravity
- hydrotropism = water
Are shoots positively or negatively gravitropic and why?
Shoots are negatively geotropic as when a shoot grown out sideways it produces an unequal distribution of auxin in the tip with more auxin on the lower side.
-this cause the lower side to grow more bending the shoot upwards
What shoots positively or negatively phototropic and why?
Shoots are positively phototropic
-when a shoot is exposed to light it accumulates more auxins on the shady side than the side exposed to the light. This causes the lower side to elongate and grow faster, bending the shoot upwards
Are roots positively or negatively gravitropic?
Positively gravitropic
-roots growing sideways will always have more auxins on its lower side but in the root the extra auxins inhabits growth. This means the cell on top elongates faster and the root bends downwards
Are roots positively or negatively phototropic?
Roots are negatively phototropic
-if roots start being exposed to light more auxins accumulate on the lower, shaded side so the root bends downwards back into the ground.
How are plant hormones used for selective weed killers?
- most weeds are broad leaves in contrast to grass etc which have very narrow leaves
- selective weedkillers use auxins that only affect broad leaves plants
- they totally disrupt their normal growth patterns which soon kills them but leaves the grass or other crops untouched
How are plant hormones used for rooting powder?
- normally if you stick a cutting of a plant in the soil they won’t grow but if you add rooting power which contain auxins they will rapidly produce roots and grow a new plant.
- this enable growth of clones of a good and rapid growing plants
- quicker as don’t need to wait for growth from seeds and more plants produces from same number of seeds
How are plant hormones used for producing seedless fruit?
- fruits with seeds normally only grow on flowering plants once pollinated
- if plant hormones such as gibberellins are applied to un-pollinated flowers the fruit will grow but the seeds won’t . Can grow larger with greater biomass
- they can slo control the time of heat when seeds germinate to ensure they all harvest at the same time
How can plant hormones be used to control the ripening of fruits?
- can be controlled either while still on the plant or during transportation.
- this allows the fruit to be unpicked while It’s still unripe (firmer and less easily damaged)
- a ripening hormone called ethene is then added and the fruit will ripen on the way to the shop and then be better to eat.
How does carbon dioxide enter the cell?
Through diffusion into the stomata from an area of high concentration to an area of low concentration
What re some advantages of positive gravitropism and phototropism?
- PG can provide strong roots for stability and means they can reach more water and mineral ions in deeper areas of soil
- PP means they can get more sunlight so more photosynthesis to provide glucose
