Organisation - Plant Cells 73-77 Flashcards
what are plants made of
made of organs like stems, roots and leaves
what are some examples of plant tissues and what is there role
5 points
1) epidermal - this covers the whole plant
2) palisade mesophyll - this is the part of the leaf where most photosynthesis happens
3) spongy mesophyll - this is in the leaf and contains big air spaces to allow gases to diffuse in and out of cells
4) xylem and phloem - they transport things like water, mineral ions and food around the plant
5) meristem - this is found at the growing tips of shoots and roots and is able to differentiate into lots of different types of plant cell
what tissues does a leaf contain
3 points
1) epidermal
2) mesophyll
3) xylem and phloem
label a leaf cell
look on page 73 of bio book
what are the epidermal tissues covered with why does this help
2 points
1) covered with a waxy cuticle
2) which helps to reduce water loss by evaporation
what are the features of the upper epidermis
2 points
1) it’s transparent
2) so that light can pass through it to the palisade layer
what are the features of the palisade layer
2 points
1) it has lots of chloroplasts
2) which means they’re near the top layer of the leaf where they can get lots of light
what are the features of the xylem and phloem in a leaf
3 points
1) they form a network of vascular bundles,
2) which deliver water and other nutrients to the entire leaf and take away the glucose produced by photosynthesis
3) they also help support the structure
how are the tissues of leaves adapted for efficient gas exchange
3 points
1) the lower epidermis of full of little holes called stomata which let CO2 diffuse directly into the leaf
2) the opening and closing of stomata is controlled by guard cells in response to the environmental conditions
3) the air spaces in the spongy mesophyll tissue increase the rate of diffusion of gases
what do phloem tubes transport
food
describe features of phloem tubes
3 points
1) made of columns of elongated living cells with small pores in the end walls to allow cell sap to flow through
2) they transport food substances made in the leaves to the rest of the plant for immediate use or for storage
3) the transport goes in both directions
what is the process of transportation in the phloem called
translocation
what do xylem tubes transport
water
describe the features of the xylem tube
1) made of dead cells joined end to end with no end walls between them and a hole down the middle
2) they’re strengthened with a material called lignin
3) they carry water and mineral ions from the roots to the stem and leaves
what is the transpiration stream
the movement of water from the roots through the xylem and out of the leaves
what is transpiration
the loss of water from the plant
where does most transpiration happen
at the leaves
describe the process of transpiration
1) its caused by the evaporation and diffusion of water from a plant’s surface
2) this evaporation creates a slight shortage of water in the leaf
3) and so more water is drawn up from the rest of the plant through the xylem vessels to replace it
4) this in turn means more water is drawn up from the roots
5) so there’s a constant transpiration stream of water through the plant
what is the purpose of a stomata
so gases can be exchanged easily
why does water escape through the stomata
2 points
1) because there is more water inside the plant than in the air out side
2) so water escapes through the stomata by diffusion
what is the rate of transpiration affected by
4 points
1) light intensity
2) temperature
3) air flow
4)humidity
how does light intensity affect the rate of transpiration
3 points
1) the brighter the light, the greater the transpiration rate
2) stomata begin to close as it gets darker. Photosynthesis can’t happen in the dark so the don’t need to be open to let CO2 in
3) when the stomata are closed, very little water can escape
how does temperature affect the transpiration rate
2 points
1) the warmer it is, the faster transpiration happens
2) when it’s warm the water particles have more energy to evaporate and diffuse out of the stomata
how does airflow affect the transpiration rate
4 points
1) the better airflow around a leaf, the greater the transpiration rate
2) if airflow around a leaf is poor, the water vapour just surrounds the leaf and doesn’t move away
3) this means there’s a high concentration of water particles outside the leaf as well as inside it so diffusion doesn’t happen as quickly
4) if there’s good airflow, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf, diffusion then happens quickly
why does humidity affect transpiration rate
3 points
1) the drier the air around a leaf, the faster transpiration happens
2) if the air is humid there’s a lot of water in it already, so there’s not much of a difference between the inside and the outside of a leaf
3) diffusion happens fastest if there’s a really high concentration in one place and a really low concentration in the other
what does a potometer estimate
1) it can estimate the rate of transpiration
2) by measuring the uptake of water by a plant because it is directly related to transpiration rate
what are guard cells
they are specialised cells shaped like kidneys which open and close the stomata
what happens to the guard cells when a plant has lots of water
2 points
1) the guard cells fill with water and go plump and turgid
2) this makes the stomata open so gases can be exchanged for photosynthesis
what happens to guard cells when the plant is short of water
2 points
1) the guard cells lose water and become flaccid making the stomata close
2) this helps stop too much water vapour escaping
how are guard cells adapted
3 points
1) they have thin outer walls and thick inner walls to make opening and closing work
2) they’re sensitive to light so they close at night to save water
3) more stomata on the underneath of a leaf because it’s shaded and cooler so less water loss
