3 Plants and food Flashcards
What do all plants contain?
Starch.
What is the main carbohydrate storage made by plants?
Starch.
Why do plants store starch?
It is a good way of storing carbohydrate because it is insoluble, compact and can be be broken down easily.
How do you test leaves for starch?
1) You remove the leaf from a plant which has been in the sunlight.
2) You de-wax the leaf using forceps in boiling water for 30 seconds.
3) Let the leaf cool down.
4) After the leaf has cooled, you immerse the leaf in boiling ethanol.
5) When the leaf has turned colourless, we remove it and put it under cold water to soften it.
6) Then put it on a tile and add iodine.
Why do you remove the leaf from a plant which has been in the sunlight?
Because the leaves contain starch from photosynthesis after glucose has been converted so we can test for it.
Why do you de-wax the leaf?
Because without de-waxing it, the leaf will not be able to absorb the solution, and the leaf needs to be de-colourised because the green colour of the leaf would hide the colour change.
Why do you wait for the leaf to cool down?
Because ethanol is highly flammable.
When do you remove the leaf from the ethanol?
When it has turned colourless or pale yellow.
What will the colour change in the iodine be if starch is present?
Orange-brown to blue black.
Under what circumstances will this work?
If the plant has had plenty of light for some hours before the test.
What is a way of de-starching a plant?
By placing it in the dark for 2 or 3 days. The plant uses up the starch stores in its leaves. De-starched plants are used to find out the conditions needed for the plant to make more starch by photosynthesis.
Where is starch only made?
in the parts of plants that contain chlorophyll.
How can you show that starch is only made in parts of plants that have chlorophyll?
By testing a leaf from a variegated plant, which has green and white areas to its leaves. The white parts of the leaf will give a negative starch test, staining yellow-brown with iodine solution. Only the green areas will stain blue black.
What does an investigation of conducting a starch test on a leaf, where the leaf was taken from a plant that had been under a bright light for 24 hours look like?
Why is the argument about chlorophyll and starch not justified?
- The leaf could have photosynthesised in the white areas and the sugars been transported elsewhere in the plant.
- The green areas may not be photosynthesised at all, but simply laying down starch from glucose made somewhere else.
Why do we assume this about chlorophyll then?
We assume this because chlorophyll is needed for photosynthesis.
What is another way of making sure that a plant can’t make starch in its leaves?
By placing it in a closed container containing a chemical called soda lime.
What does soda lime do?
This substance absorbs carbon dioxide from the air around the plant.
What happens if the plant is kept under a bright light without carbon dioixide?
It still won’t be able to make starch.
What are the factors that are needed for starch production in leaves?
- Uses carbon dioxide from the air.
- Needs light.
- Needs chlorophyll in the leaves.
- Oxygen.
When does a plant make oxygen gas?
When it is in the light.
What is starch composed of?
Long chains of glucose.
How is starch produced?
The plant first produces glucose, which is then joined together in chains to form starch molecules.
What is the formula for glucose?
C6H12O6
What are carbohydrates composed of?
Many sugar sub-units called a polysaccharide.
What is a polysaccharide?
Carbohydrate made of many sugar units, e.g. starch, which is a polysaccharide of glucose.
What is photosynthesis?
Process carried out in organisms containing chlorophyll. Light energy is used to drive reactions where carbon dioxide and water are used to make glucose and oxygen.
What is the word equation for photosynthesis?
Carbon dioxide + water (li–>ght) Glucose + oxygen
What is the chemical equation for photosynthesis?
6CO2 + 6H2O (chlo–>rophyll) C6H12O6 + 6O2
What is the role of the green pigment, chlorophyll?
To absorb the light energy needed for the reaction to take place.
What does the word equation for photosynthesis say in other words?
That photosynthesis converts light energy into chemical energy.
What is the role of chlorophyll?
To absorb the light energy needed for the reaction to take place.
What is the most adapted part of the plant for photosynthesis?
The leaves.
How are the leaves structured?
Most leaves are thin, flat structures supported by a leaf stalk which can grow to allow the blade of the leaf to be angled to receive the maximum amount of sunlight.
What are the adaptations of the leaves for photosynthesis?
- Leaves need to have a large surface area to absorb light.
- Many chloroplasts containing the chlorophyll.
- A supply of water and carbon dioxide.
- A system for carrying away the products of photosynthesis to other parts of the plant.
What are the three main sections of the leaf?
- Upper epidermis.
- Mesophyll.
- Lower epidermis.
What is the function of the two outer layers of cells (upper and lower epidermis) in relation to chloroplasts?
They have few chloroplasts and are covered by a thin layer of waxy material called the cuticle. This reduces water loss by evaporation, and acts as a barrier to the entry of disease-causing microorganisms such as bacteria and fungi.
What are the functions of the lower and upper epidermis in relation to stomata.
The lower epidermis has many holes or pores called stomata (a single pore is a stoma). Usually the upper epidermis contains fewer or no stomata. The stomata allow carbon dioxide to diffuse into the leaf, to reach the photosynthetic tissues. They also allow oxygen and water vapour to diffuse out. Each stoma is formed as a gap between two highly specialised cells called guard cells, which can change their shape to open or close the stoma.
What does the lower epidermis contain?
Many holes or pores called the stomata.
Which has more stomata the lower, or upper epidermis?
Lower. The upper usually contains fewer or no stomata.
What are the functions of the stomata?
The stomata allows carbon dioxide to diffuse into the leaf, to reach the photosynthetic tissues. They also allow oxygen and water vapour to diffuse out.
What are the stomata encircled by?
Guard cells.
What do guard cells do?
They can change their shape to open or close the stoma.
What is just below the upper epidermis?
The palisade mesophyll layer.
What is the palisade mesophyll layer?
It is a tissue made of long, narrow cells, each containing hundreds of chloroplasts, and is the main site of photosynthesis.
What is the function of the palisade mesophyll layer?
In the middle of the leaf are two layers of photosynthetic cells called the mesophyll. Just below the upper epidermis is the palisade mesophyll layer. The palisade cells are close to the source of light, and the upper epidermis is relatively transparent, allowing light to pass through to the enormous numbers of chloroplasts which lie below.
Where are the palisade cells located?
They are close to the source of light and the upper epidermis is relatively transparent, allowing light to pass through to the enormous number of chloroplasts which lie below.
Where is the spongy mesophyll located?
Below the palisade layer.
What is the spongy mesophyll?
It is a tissue made of more rounded, loosely packed cells, with air spaces between them.
What is the difference with the cells in the spongy mesophyll and palisade cells?
The cells in the spongy mesophyll also photosynthesise, but have fewer chloroplasts than the palisade cells.
What do the cells in the spongy mesophyll do?
They form the main gas exchange surface of the leaf, absorbing carbon dioxide and releasing oxygen and water vapour.
What function do the air spaces in the spongy mesophyll have?
The air spaces allow these gases to diffuse in and out of the mesophyll.
How are water and mineral ions supplied to the leaf?
Through the xylem.
What does the xylem do?
This forms a continuous transport system throughout the plant. Water is absorbed by the roots and passes up through the stem and through veins in the leaves in the transpiration stream.
What is the transpiration stream?
It is the passage of water and minerals through the roots, stem and leaves of a plant.
How does water get to the leaves?
In the leaves, the water leaves the xylem and supplies the mesophyll cells.
What is the function of the phloem?
The products of photosynthesis, such as sugars, are carried away from the mesophyll cells by another transport system - the phloem.
Apart from that, what else does the phloem do?
The phloem supplies all other parts of the plant, so that tissues and organs that can’t make their own food receive products of photosynthesis. The veins in the leaf contain both xylem and phloem tissue, and branch again and again to supply all parts of the leaf.
Why do graphs showing the rate of photosynthesis with a certain factor plateau?
It is because some other factor needed for photosynthesis is in short supply, so that increasing the light intensity (a specific factor) does not affect the rate any more.
What is a limiting factor?
Component of a process or reaction that is in ‘short supply’, so that it prevents the rate of reaction from increasing.
Which is the factor which usually holds back the rate of photosynthesis?
The concentration of carbon dioxide in the air.
What happens if a plant is put in a closed container with a higher than normal rate of carbon dioxide?
It will photosynthesise at a faster rate, but will not keep photosynthesising forever as there could be a limiting factor, such as light or temperature.
What happens if there is both a high light intensity and a high level of carbon dioxide?
The temperature may limit the rate of photosynthesis.
In reference to reactions, how do certain factors limit the rate of photosynthesis?
By limiting the rate of chemical reactions in the leaf.
How do you measure the rate of photosynthesis using pondweed?
You can measure the rate of photosynthesis of a plant by measuring how quickly it produces oxygen. With an aquatic plant such as a pond weed, bubbles of oxygen are released into the water around the plant.
What is the apparatus needed for this experiment?
- Lamp.
- Thermometer.
- Pondweed.
- Water.
- Ruler.
How exactly can we see the rate of photosynthesis in the water?
If the bubbles formed per minute are counted, this is a measure of the rate of photosynthesis of the plant. It is easiest to count the bubbles if the cut piece of weed is placed upside down in a test tube. A small paperclip attach the bottom of the piece of weed makes it sink.
How do we provide light to the plant?
With the lamp. The light intensity is changed by moving the lamp, altering the distance between the lamp and the pond weed,
How do we keep the temperature constant?
The beaker of water keeps the temperature of the plant constant.
What is glucose?
A single sugar unit.
What can plant cells do with glucose?
Convert it into other sugars.
What other sugars do the plants convert glucose into?
- Fructose.
- Sucrose.
What can glucose be converted into?
- Sucrose for transport.
- Starch for storage.
- Cellulose for cell walls.
- Proteins and DNA.
(mineral ions from soil - nitrates, phosphates). - Lipids - oil in seeds.
- Chlorophyll.
(magnesium ions from soil).
What kind of minerals are absorbed from the soil water?
- Nitrate ions.
- Phosphate.
- Potassium.
- Magnesium ions.
Why is phosphorus needed?
For plant cells to make many important compounds, including DNA.
Why are potassium ions needed?
They are required for enzymes in respiration and photosynthesis to work.
Why is magnesium needed?
It forms part of the chlorophyll molecule.
What does a plant take from soil for growth?
Only water and mineral ions.
What is said about water cultures?
Plants can be grown in soil-free cultures (water cultures) if the correct balance of minerals is added to the water.
What is Knop’s solution?
0.8g calcium nitrate
0.2g magnesium sulfate
0.2g potassium nitrate
0.2g potassium dihydrogenphosphate
(trace) iron (III) phosphate
What is special about Knops solution?
These chemicals provide all of the main elements that the plant needs to make proteins, DNA and chlorophyll, as well as other compounds, from glucose.
What is Knops solution called?
A complete culture solution.
What happens if you were to make a similar solution but you replace magnesium sulfate with calcium sulfate?
This would produce a culture solution which was deficient (lacking) in magnesium, so you could then grow plants in the complete and deficient solutions, and compare the results
What does a simple water culture apparatus look like?
Under what conditions does a simple water culture method kept under?
The plant is kept under a bright light, so that it can photosynthesise. The covering around the flask prevents algae from growing the culture solution. The aeration tube is used for short periods to supply the roots with oxygen for respiration of the root cells, since some ions are taken up by active transport.
Why are methods like these useful?
Using methods like this, it soon becomes clear that mineral deficiencies result in poor plant growth.
What does a shortage of a particular mineral result in?
In particular symptoms in the plant, called a mineral deficiency disease.
What is an example of a mineral deficiency disease?
Lack of magnesium means that the plant won’t be able to make chlorophyll, and the leaves will turn yellow.
What are the mineral ions needed by plants?
- Nitrate.
- Phosphate.
- Potassium.
- Magnesium.
What does nitrate do?
Making amino acids, proteins, chlorophyll, DNA and many other compounds.
What are nitrate deficiency symptoms?
Limited growth of plant; older leaves turn yellow.
What does phosphate do?
Making DNA and many other compounds; part of cell membranes.
What are phosphate deficiency symptoms?
Poor root growth; younger leaves turn purple.
What does potassium do?
Needed for enzymes for respiration and photosynthesis to work.
What are potassium deficiency symptoms?
Leaves turn yellow with dead spots.
What does magnesium do?
Part of chlorophyll molecule.
What are magnesium deficiency symptoms?
Leaves turn yellow.
What is osmosis?
It is the name of a process by which water moves into and out of cells.
What is an artificially partially permeable membrane?
Viskin tubing.
How does visking tubing work?
Visking tubing has microscopic holes in it, which lets small molecules like water pass through it, but is not permeable to some larger molecules.
How can you show the effects of osmosis?
By filling a visking tubing ‘sausage’ with concentrated sucrose solution, attaching it to a capillary tube and placing the visking tubing in a beaker of water.
What happens to the water level in the capillary tube?
The water level in the capillary tube rises as water moves from the beaker to the inside of the visking tube.
PRACTICAL ONION EPIDERMIS CELL.
MORE ABOUT OSMOSIS (PAGE 154)
PRACTICAL INVESTIGATING THE EFFECTS OF OSMOSIS ON POTATO TUBER TISSUE.
Why aren’t the stomata on the upper leaf surface?
The leaf would lose too much water as the stomata would be exposed to too much sunlight, which would produce a high rate of evaporation from them. There is also less air movement on the underside of leaves. This is an adaptation so water loss is kept at a minimum.
What is the percentage change equation?
Change in mass
———————- x100
Starting mass
TRANSPORT IN THE XYLEM
TRANSPORT IN THE PHLOEM
STRUCTURE OF A STEM
TROPISMS
