Paper 1: Topic 2 Organisation - Plant tissues, organs and systems (IV form) Flashcards
Why do plants need a transport system?
They are too large for materials to simply diffuse in and out and meet the demand of the plant
Give three examples of a plant organ
- Leaf
- Stem
- Root
Where is sucrose transported to?
The sinks e.g. roots
This is where the sucrose is converted to starch or other molecules for storage
What causes the stomata to open?
The guard cells absorb water
By osmosis
This causes the guard cells to become turgid
This causes the stomata to open and widen
What is the role/function of the palisade mesophyll layer in the leaf?
These cells are specialised to contain many chloroplasts
Hence they carry out photosynthesis
What is the role/function of the stoma in the leaf?
- Stomata can widen and narrow to control how much gas exchange occurs i.e. intake of carbon dioxide and loss of oxygen
- and to control how much water vapour is lost from the leaf during transpiration
Summary: Control gas exchange and water vapour loss
Which direction does xylem transport materials?
ONLY up the plant i.e. one way movement
From the roots to the stem and the leaves
What is the role/function of the air spaces in the leaf?
Site for gas exchange:
a) oxygen diffuses out of the mesophyll cells into the air spaces
b) carbon dioxide diffuses from the air spaces into the mesophyll cells
Which process of transport uses phloem tissue?
Translocation
How does transpiration take place?
Hint: there are 3 key stages
- Water vapour evaporates out of the leaf through the stomata
- This generates a transpiration pull - which pulls water up through the plant in the xylem
- The water that is lost from the base of the plant is then replaced as root hair cells absorb more water from the soil by osmosis
What is the role/function of the guard cell in the leaf?
Specialised cells that can take in water or lose water by osmosis
Depending on how much water they contain they can open and close pores (stomata)
Control gas exchange and water vapour loss
What assumption is made when using a potometer to measure the rate of transpiration?
That the rate of water vapour loss from the plant is the SAME as the rate of the water uptake by the plant
What causes transpiration?
Transpiration is a side effect of photosynthesis
When the plant is photosynthesising it opens its stomata to allow carbon dioxide to diffuse in
This then allows the water vapour in the air spaces of the leaf to diffuse out causing the transpiration stream
What materials does xylem transport?
Water and dissolved mineral ions
How does the water vapour exit the leaf?
By diffusion
Remember water vapour is a gas!
Describe and explain how root hair cells adapted for the uptake of mineral ions
Many mitochondria are present in each root hair cell
The mitochondria produce ATP
The ATP can then be used/broken down to release energy
Thsi energy is used for the active transport of mineral ions into the cell
What conditions cause the rate of transpiration to INCREASE?
Higher temperature
Faster wind speed
Lower air humidity (dier air)
What materials does phloem transport?
Sucrose (a specialised carbohydrate made from glucose)
Where is the xylem and phloem located in plants?
In vascular bundles
What is the role/function of the phloem in the leaf?
Specialised cells forming a tissue responsible for transporting dissolved sugars up and down the plant
Located in the vascular bundles (veins)
What causes the stomata to close?
The guard cells lose water
By osmosis
This causes the guard cells to become plasmolysed
This causes the stomata to narrow and close
What is the main role of stomata?
To allow gas exchange between the leaf the atmosphere
How is the rate of transpiration usually investigated in a laboratory?
Using a potometer
Give 4 key features of xylem
- The cells are dead
- The cells are hollow (no cytoplasm)
- The cells have lignin around them (to make them waterproof and strengthen the cell)
- The cells are joined end to end to form continuous hollow columns
Where is sucrose transported from?
The source i.e. the leaves (where the sucrose is made)
What is the role/function of the upper epidermis in the leaf?
Specialised cells which are thin and flat It is transparent to enable light to pass through them easily to reach the palisade mesophyll tissue
What 3 gases diffuse in and out of the leaf? For each gas state which direction it diffuses.
Oxygen - diffuses out of the leaf
Carbon dioxide - diffuses in to the leaf
Water VAPOUR - diffuses out of the leaf
Why is it incorrect to say a potometer measures the rate of transpiration?
The potometer doesn’t actually measure the amount of water vapour that is lost from the plant
Instead it actually measure the volume of water taken up by the plant
How do water molecules move through the xylem during transpiration?
As a continuous column of water molecules
What is the role/function of the chloroplast in the leaf?
Site where photosynthesis occurs
Chloroplast contain a special pigment called chlorophyll that is essential for photosynthesis
Which direction does phloem transport materials?
Up AND down the plant
i.e. two way movement
Why does a lower humidity increase the rate of transpiration?
The lower the humidity of the air outside the stomata the greater the concentration gradient between the inside and the outside of the leaf
This will cause the water vapour to diffuse out of the leaf quicker due to a steeper concentration gradient
How do plants produce glucose?
Photosynthesis
What is the role/function of the lower epidermis in the leaf?
Found on the underside of the leaf Location of stomata and guard cells
Why do xylem cells have lignin?
To make them waterproof and strengthen the xylem cell
What is translocation?
- The movement of sucrose and dissolved sugars
- up and down the plant
Which process of transport uses xylem tissue?
Transpiration
What are stomata?
Tiny pores found between two guard cells
What environmental conditions affect the rate of transpiration?
Temperature
Wind speed
Humidity of the air
What is transpiration?
The loss of water VAPOUR by diffusion from the stomata found on the underside of the leaf
Give 4 key features of phloem
- The cells are living and contain cytoplasm and cell sap
- The cells form elongated columns
- The ends of the cells are partially broken down to form sieve plates
- Phloem tissue consists of sieve tube elements and companion cells
Why do phloem cells have perforated end walls? (2)
- So that cell sap can move from one phloem cell to the next through pores in the end walls
- With less resistance
Why does a higher wind speed increase the rate of transpiration?
The wind will blow the water vapour that is under the leaf away from the leaf
This will then maintain the concentration gradient between the inside and the outside of the leaf
This then causes more water vapour to evaporate out of the leaf by diffusion
Describe and explain two ways in which root hair cells adapted for the uptake of water?
Description 1 = long extensions to the cell membrane and cytoplasm
Explanation 1 = increases the surface area for osmosis to occur over
Description 2 = thin cell wall
Explanation 2 = decreases the distance for osmosis to occur
What are the two tissues that make up the plant transport system?
Xylem
Phloem
Why is it incorrect to assume that the rate of water vapour loss from the plant is the SAME as the rate of the water uptake by the plant?
Some of the water taken up could be used in photosynthesis or used in other chemical reactions
Why does the plant need to make glucose?
All living cells require glucose for respiration to produce ATP
The ATP is then used to release energy so other chemical reactions it the cell can occur
What is the role/function of the xylem in the leaf?
Specialised cells forming a tissue responsible for transporting water and dissolved ions up the plant
Located in the vascular bundles (veins)
What are the two different types of cells that make up the tissue phloem?
Phloem sieve tubes
Companion cells
What is the role/function of the waxy cuticle in the leaf?
Thin protective layer made of a waxy substance
Prevents the leaf from being damaged from the heat of the sun’s rays
Also helps reduce water loss
Also helps protect the leaf from damage by insects etc
How do the stomata open and close?
The size of the stomata are controlled by the guard cells
Why do higher air temperatures increase the rate of transpiration?
The higher the temperature the more water that will evaporate off the spongy mesophyll cells into the air spaces in the leaf
This will increase the concentration of water vapour in the air spaces
This will cause the water vapour to diffuse out of the leaf via the stomata quicker due to a steeper concentration gradient
What is the role/function of the spongy mesophyll layer in the leaf?
Specialised cells which contain only a few chloroplasts but are more spherical in shape
Allow pockets of air spaces to form between them which are essential for gas exchange
Give 2 reasons why it is important that the waxy cuticle is transparent
- To enable light to pass through the cuticle
- So that the light can reach the chloroplasts in the pallisade mesophyll cells
