Topic 6- Plants Flashcards
(32 cards)
Describe the practical to investigate how light intensity affects the rate of photosynthesis
Apparatus:
Gas syringe
Light Source
Canadian pondweed
Ruler
Conical flask filled with water
Bung
Method:
The gas syringe should be empty to start with
A source of white light is placed at a specific distance from the pondweed
The pondweed is left to photosynthesise for a set amount of time
As it photosynthesises the oxygen will be collected in the gas syringe, so you can measure the volume of oxygen produced
The experiment is repeated with the light source at different distances from the pondweed
The rate of oxygen production can be calculated (volume produced / time taken)
Describe how light affects the rate of photosynthesis
At first as the light intensity increases, the rate of photosynthesis increases proportionally
Up to a certain point, increasing the light intensity won’t make a difference, it will be temperature or CO2 which is the limiting factor
Light intensity = 1/d2
Describe how carbon dioxide affects the rate of photosynthesis
At first as the lCO2 increases, the rate of photosynthesis increases proportionally
Up to a certain point, increasing the CO2 won’t make a difference
Describe how temperature affects the rate of photosynthesis
As the temperature increases, the rate of photosynthesis also increases, however if the temperature gets too high, enzymes will denature and the reaction will stop (45 degrees C)
Describe how root hair cells take in minerals and water by active transport
The cells on the surface of plant roots grow into hairs, which stick out into the soil
Each branch of the root is covered in millions of these microscopic haits
This gives the plant a large surface area for absorbing water and mineral ions
The concentration of mineral ions is usually higher in the root hair cells than in the soil around them, so mineral ions are absorbed by active transport and water is absorbed by osmosis
What are phloem tubes made of?
Phloem tubes are made of columns of elongated living cells with small pores in the end walls to allow stuff to flow through
What do phloem tubes transfer?
Food (sucrose for example)
How does the phloem transport substances to the rest of the plant?
It transfers food to the rest of the plant for immediate use or for storage, this is done via the process of translocation and it requires energy from respiration, the transport goes in both directions
What are xylem tubes made of?
Xylem tubes are made of dead cells joined end to end with no end walls in between them and a hole down the middle, they are strengthened by liginin
What do xylem tubes do and how do they do it?
They carry water and mineral ions from the roots to the stem and the leaves, this is known as transpiration and the xylem makes up a part of the transpiration stream
What is transpiration?
Transpiration is the loss of water from the plant
What is transpiration caused by?
The evaporation and diffusion of water from a plant’s surface. Most transpiration happens at the leaves
How does transpiration work?
The loss of water creates a slight shortage of water in the leaf and so more water is drawn up from the rest of the plant through the xylem vessels to replace it
This means that more water is drawn up from the roots and so there’s a constant transpiration stream of water through the plant
The transpiration stream carries mineral ions that are dissolved in the water along with it
Explain how the stomata regulate the size of the pore
When the guard cells become turgid (swollen with water) the stomata are open, however when they are flaccid (low on water and limp) the stomata is closed
How does light intensity affect transpiration rate?
The brighter the light, the greater the transpiration rate. The stomata begins to close when it gets darker, photosynthesis can’t happen in the dark, so they don’t need to be open to let CO2 in. When the stomata are closed, very little water can escape
How does temperature affect rate of transpiration
The warmer it is, the faster transpiration occurs because water particles have more energy to evaporate and diffuse out of the stomata
How does air flow affect rate of transpiration
The better the air flow around a leaf, the greater the transpiration rate. If air flow around a leaf is poor, the water vapour just surrounds the leaf and doesn’t move away. Meaning there is a high concentration of water particles outside the leaf as well as inside it, so diffusion does not happen as quickly
What is the experiment to estimate transpiration rate?
You can use a potometer which measures water uptake by a plant
How is the palisade layer adapted for photosynthesis?
It has lots of chloroplasts, this means they are near the top of the leaf where they can get the most light
How is the upper epidermis adapted for photosynthesis?
It is transparent so that light can pass through it to the palisade layer
How is the spongy mesophyll adapted for photosynthesis?
It contains air spaces which increase the rate of diffusion of gases into and out of the leaf’s cells
How is the waxy cuticle adapted for photosynthesis
It is thick which helps to reduce water loss by evaporation
What are some adaptations of plants to live in extreme environments?
Small leaves to reduce transpiration
Spines to stop animals eating the plant to get water
Thick waxy cuticles to reduce water loss
Thick stem to store water
What is the function of auxins?
They promote growth in shoots but inhibit growth in roots
