Topic 2 The World of Plants. Standard Grade Biology. World of Plants is divided into: A- Introducing plants B- Growing plants (Pollination, Fertilisation, Asexual reproduction) C- Making food. Plants- the first link. Workbook Activity. p 54 Food webs and plants.
Standard Grade Biology
A- Introducing plants
B- Growing plants (Pollination, Fertilisation, Asexual reproduction)
C- Making food
p 54 Food webs and plants
Plants are the link between the energy in the sun being converted into a form which animals can eat and get the energy to survive…
The process by which plants do this is called:
All living things respire all the time to release energy from their food in a process called:
carbon dioxide + water glucose + oxygen
Plants make their own food, glucose, by photosynthesis.
It only happens during the daytime when there is light available.
This happens in plant cells containing the chemical chlorophyll (green-coloured) which traps the light energy.
The plants have captured light energy and turned it into a store of chemical energy (glucose).
More on the uses for glucose shortly…
Workbook Problem Solving
p 81 Making a starch print
Which parts of the leaf do you think will go blue- black?
Why do parts that were not covered contain starch?
Workbook Problem Solving
p 76 Plants and greenhouses
Does the leaf contain starch? Why/ why not?
Has the plant carried out photosynthesis?
What would be your control plant’s conditions?
(Hint: a control plant should have everything it needs for photosynthesis including carbon dioxide).
CO2 is converted into glucose by photosynthesis.
Raw material for growth, repair and replacement of damaged parts
Used immediately to provide energy source for respiration
Energy used to turn sugars, nitrates & other nutrients into amino acids which build up proteins
To make fats & oils (energy stored in seeds)
Energy stored as sucrose (in fruit)
Energy storedasstarch (in leaves, seeds, roots and tubers)
To make cellulose, the main structural material in cell walls
p 70 Changes in carbohydrate
What colour change would you expect if sugar was present?
b) Write an explanation of your results.
You need to know the plant experiments in detail, explain the different steps, and results, in each one.
starch is present.
Repeat the starch test but this time use a variegated leaf from a geranium plant.
Variegated means that a plant has coloured and white parts on its leaves.
Do the green parts contain chlorophyll? Do the white bits? Which do you think will test positive for starch?
A tree is planted in a meadow.After 20 years it has grown into a big tree, weighing 250kg more than when it was planted.
all the time
glucose + oxygen carbon dioxide (CO2) + water
carbon dioxide + water glucose + oxygen
During the day:
Oxygenreleased by photosynthesis is greater than the amount of oxygen used up in respiration.
CO2 used in photosynthesis is greater than the amount of CO2 produced by respiration.
Fill a test tube with water too and cover the top as you place it upside down inside the jar.
Take a runner and feed it up inside the test tube.
Leave in direct sunlight for a few hours
A bubble of oxygen gas should form at the top of the test tube as it photosynthesises
p 64-65 Elodea bubbler expt
Plants’ waste product- oxygen- is essential for animal life.
1. What does a plant need for photosynthesis?
Carbon dioxide, water, chlorophyll, light.
2. What does a leaf produce during photosynthesis?
3. What is chlorophyll?
A green pigment which absorbs the sun’s energy
4. How do the leaves obtain water?
Through the roots (and xylem tubes by osmosis
5. How does the plant obtain carbon dioxide?
From the air (through stomata)
6. List 3 uses of the glucose produced by photosynthesis?
Cellulose (structural), starch (storage), energy
7. Name the storage form of carbohydrate in a leaf.
Read through the file and take some short notes to summarise the life of a leaf
Leaves are the organs of photosynthesis and make all the food for a plant.
Collect the handout ‘Leaf structure’ and add labels/notes.
1. The waxycuticle is a waterproof layer which cuts down water loss by evaporation.
2. The upper cells of the leaf make up the epidermis.
They are transparent so light passes straight through them into the next layer of cells…
Chloroplasts contain chlorophyll which is the chemical which absorbs the sun’s light energy.
Hence this is where most photosynthesis occurs.
The spongy layer (spongy mesophyll) contains rounded cells with many air spaces allowing CO2 to circulate and reach the palisade cells, while O2 leaves.
p 66-67 Leaf surface and thickness
p67 Leaf layer cards- matching
p78 How many stomata?
p79 Water content and dry weight.
p85 Use of cobalt choride paper
Bioviewers Box 79
The leaf of a flowering plant
Leaf epidermis with stomata- scanning electron microscope
On the lower surface of the leaf there are tiny pores called stomata (singular- stoma) which open and close.
Stomata let CO2 diffuse in.
Water vapour and oxygen (O2) move out.
p 62 Leaf surfaces
Stomata have guard cells surrounding them to control their opening & closing.
When there is plenty of water (daytime) the guard cells are turgid and curved.
This opens the stomata and water can escape.
Workbook Activity PS
p63 stomata behaviour p82 & 83 Leaf balance
When there is little water the guard cells are flaccid and less curved.
This closes the stomata and keeps waterin the leaf. This happens at night.
Flat leaf blade
Has large surface area
Absorbs as much sunlight & CO2 as possible
CO2, reaches inner cells easily
Vast network of veins
supplies all parts of the plant with essential substances
Most in lower surface of leaf
Gas & water exchange
Workbook Problem Solving
p 80 Ringing a plant
Leaf veins (and roots and stems) contain the xylem and phloem tubes in vascular bundles.
They run throughout the plant, transporting various substances up and down them.
p 61 Food transport diagram
Giant redwood trees carry water & nutrients over 100m from the soil
Water passes from the soil into root hairs by osmosis
HOW DOES IT HAPPEN?
Transpiration is the evaporation of water from the leaves of a plant.
The transpiration stream is the movement of water up the xylem (roots-stem-leaves).
Why?So it is not blown / knocked over
How? The roots spread out over a large area to counterbalance the structures above the soil.
This also helps plants find water.
Many tiny hairs branch off the main root
Why?To take up substances to survive.
How? Roots have tiny hairs on their surface which increases their surface area to maximise absorption.
A root hair shown under a microscope
Root hair cell
Why?Water is a raw material for photosynthesis.
How? Root hairs increase surface area.
In flowering plants there are separate transport systems for water and nutrients.
Substances are transported in vascular bundles made up of the xylem and the phloem.
Transportswater and mineralsupwards from the roots to the stem and leaves.
The Xylem is made of dead cells joined into hollow tubes. They have thick strong walls made of lignin which give the plant support.
e.g. sugars made by photosynthesis, all round the plant.
The sugars are transported all round the plant especially to growing regions and the storage organs.
Phloem cells are alive and are made of 2 types of cells; sieve tubes and companion cells.
Sieve cell end walls have holes (pores) in them. Companion cells contain the cell nuclei.
p 72 Structure of xylem and phloem.
Leaf Veins are Vascular Bundles.
Vascular bundlesare composed ofXylem, PhloemandFibres which support and protect the xylem and phloem.
p 73 Looking at xylem
Vascular Bundles in sugar cane.
Below: detail of one bundle
p 60 Water transport in plants
Bioviewers Box 78
The stem of a flowering plant
The positions are different in stems compared to roots. In a stem they are round the outside.
p 68-69 Structure stem, root
In roots they are found in the centre.
Light + chlorophyll
Carbon dioxide + water oxygen + glucose
If there are inadequate ingredients photosynthesis will stop or slow down.
Hence, photosynthesis cannot take place due to lack of light.
Light is the limiting factor.
Often this sort of information is shown in a graph…
p 74 The effect of increasing carbon dioxide
p75 The effect of increasing temperature
ALight intensity is limiting the rate of reaction
BCO2 is limiting the rate of reaction
CThe difference between the lines is due to different temperatures.
1. How is glucose carried from the leaves to every part of the plant?
Transported in phloem tubes (water in xylem)
2. Give 2 structural features of a leaf that make it a good design for photosynthesis.
Large surface area, thin, stomata, veins
3. Why do you think that the palisade cells are near the surface of the leaf?
To absorb as much sunlight as possible in chloroplasts
4. Name the cells that surround the stomatal openings.
5. The spongy mesophyll cells are loosely arranged. Explain the significance of this.
Large spaces between cells allow gases to diffuse quickly
6. Which 3 factors limit the rate of photosynthesis?
Quantity of light, carbon dioxide, temperature
1. Yellowing of leaves
2. Poor fruit growth.
Lack of Magnesium causes leaves to turn yellow from the bottom of the plant upwards
Leaf from the top of a plant
Leaf from the bottom of a plant
1. Purpling of leaves
2. Poor root growth
3. Small plant size
Copy out the diagrams from p63 Co-ordinated Biology (second Edition) showing nutrient deficiency in plants
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