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Topic 2 The World of Plants

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1 Topic 2 The World of Plants
Standard Grade Biology Topic 2 The World of Plants

2 C- Making food World of Plants is divided into: A- Introducing plants
B- Growing plants (Pollination, Fertilisation, Asexual reproduction) C- Making food

3 Plants- the first link Workbook Activity Photosynthesis Respiration
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… Workbook Activity p 54 Food webs and plants The process by which plants do this is called: Revise Environment subtopic How It Works, terms- producer, consumer etc. Teachers notes LO- explain the dependence of food webs on photosynthesis. Interpretation- all living things get energy from food. Plants use energy from the sun to make food. Animals get their food, and their energy, by eating plants or animals which have eaten plants. Food webs therefore rely on plants to supply their energy. Photosynthesis All living things respire all the time to release energy from their food in a process called: Respiration

4 carbon dioxide + water  glucose + oxygen
Plant survival Plants make their own food, glucose, by photosynthesis. It only happens during the daytime when there is light available. Light energy carbon dioxide + water  glucose + oxygen chlorophyll Raw materials Products 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). SQA LO Describe the process of photosynthesis in terms of raw materials and products Interpretation- photosynthesis combines CO2 and H2O to produce glucose (sugar) and oxygen. Chlorophyll found in the chloroplasts of plant cells is essential for photosynthesis. Chlorophyll traps the light energy from the sun. Light energy from the sun is used to combine CO2 and H2O AND State that green plants convert light energy to chemical energy using chlorophyll Interpretation- the process by which green plants make their own food is called photosynthesis. A process by which light energy is converted into chemical energy. Which takes place in the Leaves of green plants More on the uses for glucose shortly…

5 Is light needed for photosynthesis?
Take a de-starched geranium plant (24h in dark).  Cover part of a leaf with some tin foil (this prevents light getting through). Leave the plant in sunlight for a few hours. Test the leaf for starch. Common steps in expts: - leave in darkness for 24 hours- to destarch plant Variable factor tested- experimental variable tested such as light, temp, chlorophyll Leave for time- in light to allow time for plant to make starch Test for starch- show if photosynthesis has made starch.

6 Is carbon dioxide needed for photosynthesis?
Take a de-starched geranium plant Enclose it in a plastic bag with a chemical that absorbs carbon dioxide. (e.g. soda lime or sodium hydroxide pellets). Leave the plant in sunlight for a couple of hours. Test the leaf for starch.

7 Is light needed for photosynthesis?
Questions: 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 81 Making a starch print

8 Is carbon dioxide needed for photosynthesis?
Questions: 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). Workbook Problem Solving p 76 Plants and greenhouses CO2 is converted into glucose by photosynthesis.

9 Mans’ uses of plant glucose

10 Plants’ uses of plant glucose
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) Glucose Energy stored as sucrose (in fruit) Energy stored as starch (in leaves, seeds, roots and tubers) To make cellulose, the main structural material in cell walls SQA LO State that green plants make their own food which may be stored as starch. Interpretation- green plants are able to make their own food. Green plants make food in the form of sugar. The sugar made by the plant is either used straight away or converted to starch and stored

11 Glucose molecule Workbook Activity p 70 Changes in carbohydrate
SQA- Describe the fate of CO2 as structural and storage carbohydrates in plants and as energy sources. Interpretation- sugar made by plants from CO2 and H2O can be: a) Stored as starch until needed b) Used to supply energy c) Used as building material (eg cellulose in plant cell walls). Workbook Activity p 70 Changes in carbohydrate

12 Activity – Testing a plant for sugar
Put a piece of raw onion in a pestle and mortar. Grind it with a little sand and 10cm3 of water. Filter the liquid into a test tube Heat the liquid with 10 drops Benedict’s solution in a water bath What colour change would you expect if sugar was present? b) Write an explanation of your results. Sugar is soluble (dissolves in water). When it is converted into starch it is insoluble so can be stored. Starch can be converted (by enzymes) back into glucose when the plant needs it. REVISE Environment topic, Control and management? The CARBON CYCLE. You need to know the plant experiments in detail, explain the different steps, and results, in each one.

13 Activity -Testing a leaf for starch
Dip a leaf into boiling water for about a minute (to soften it). Turn off the Bunsen burner. Put the leaf into a test-tube of ethanol (to remove chlorophyll). Stand the test-tube in a beaker of hot water for about 10 minutes. Wash the leaf in cold water. Spread the leaf out flat on a petri dish and cover it with iodine solution (tests for starch). If the leaf goes blue-black, starch is present. Why Boil in water to soften and kill leaf Boil in alcohol to remove chlorophyll Rinse in water to soften leaf Add iodine, to test for starch, goes black.

14 Activity -Testing a leaf for chlorophyll
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?

15 From little acorns do great oaks grow…
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. Where do the extra 250kg come from? Explain your answer as fully and scientifically as you can.

16 Gas Balance Respiration Photosynthesis all the time
glucose + oxygen  carbon dioxide (CO2) + water Photosynthesis daylight only carbon dioxide + water  glucose + oxygen During the day: Oxygen released 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.

17 Take a runner and feed it up inside the test tube.
                                                                                                                                          Fill a jar with water. 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 Source Result? A bubble of oxygen gas should form at the top of the test tube as it photosynthesises

18 Summary of Photosynthesis
Plants’ waste product- oxygen- is essential for animal life. Workbook Activity p Elodea bubbler expt

19 Quick Quiz 1 1. What does a plant need for photosynthesis?
Carbon dioxide, water, chlorophyll, light. 2. What does a leaf produce during photosynthesis? Oxygen, glucose 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. Starch.

20 A leaf in time Library activity
Read through the file and take some short notes to summarise the life of a leaf Source:

21 Leaves… Leaves are the organs of photosynthesis and make all the food for a plant. We will look at: Outer layers (top & bottom) Inner structure including veins (its transport system)

22 Internal structure waxy cuticle mesophyll SQA- Describe the external features and internal structure (epidermis, mesophylls, veins) of a leaf in relation to its function in gas exchange Interpretation- a leaf has a large surface area to allow the maximum amount of light to enter the leaf. And to expose it to as much air as possible. A leaf is thin to allow CO2 to pass quickly to the cells which carry out photosynthesis. And to allow O2 to leave the leaf as quickly as possible. Thin to allow sunlight to penetrate to all cells. Outer layer of cells on a leaf is called the epidermis. Epidermis is transparent to allow light through. Epidermis contains stomata which allow gases in and out. Top layer of the cells in a leaf is called the palisade mesophyll layer The layer of cells below the palisade layer is called the spongy mesophyll. The spongy mesophyll cells are loosly packed with large air spaces to allow CO2 and O2 to get to and from cells quickly. Leaf veins are made up of xylem and phloem within a short distance of every mesophyll cell to carry food away from and water to, leaf cells. Collect the handout ‘Leaf structure’ and add labels/notes.

23 Outer layer- upper surface
1.waxy 2. Epidermis transparent so no chlorophyll 1. The waxy cuticle 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…

24 The palisade layer contains cells with lots of chloroplasts.
mesophyll 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.

25 Workbook Activities Problem Solving Bioviewers Box 79
p Leaf surface and thickness p67 Leaf layer cards- matching Problem Solving 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

26 Outer layer- bottom surface
Leaf epidermis with stomata- scanning electron microscope SQA- State that plants take in carbon dioxide from the air through stomata which can open and close Interpretation- stomata are tiny pores on the surface of a leaf. Carbon dioxide enters the leaf through stomata. During the day stomata are open. During the night stomata are closed. Know that water vapour is lost through stomata 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.

27 Stomata- open Workbook
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. SQA- State that water vapour is lost through stomata. Interpretation- the tiny pores (stomata) on the surface of a leaf allow water to be lost from the leaf. Workbook p 62 Leaf surfaces

28 Stomata- closed Workbook Activity PS
When there is little water the guard cells are flaccid and less curved. This closes the stomata and keeps water in the leaf. This happens at night. GUARD CELLS are only part of lower epidermis which contain chloroplasts They control gas exchange by closing stomata in darkness, or when too much water is being lost. Workbook Activity PS p63 stomata behaviour p82 & 83 Leaf balance

29 General structure Flat leaf blade Thin Vast network of veins Stomata
Has large surface area Absorbs as much sunlight & CO2 as possible Thin CO2, reaches inner cells easily Vast network of veins supplies all parts of the plant with essential substances Structural support Bioviewer slide set? Prepared microscope slides? Stomata Most in lower surface of leaf Gas & water exchange

30 Workbook Problem Solving
Leaf veins 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. Workbook Problem Solving p 80 Ringing a plant

31 Transport systems used for?
Plants need to allow: Gases to get in and out of the leaves. Water and nutrients to move into the plant from the soil. Glucose made in photosynthesis to be carried to the rest of the plant. SQA LO Explain why plants need transport systems Interpretation- water is required for photosynthesis. Food manufacture in the leaves is needed for growth and energy by the plant. Workbook Activity p 61 Food transport diagram Giant redwood trees carry water & nutrients over 100m from the soil

32 Roots Roots have specialised cells called root hair cells, which are long and thin providing a large surface area for the uptake of water and minerals. SQA LO

33 Into the root hair cell Water passes from the soil into root hairs by osmosis DEFINITION Osmosis is the net diffusion of water across a partially permeable membrane, from a solution with a high water concentration (HWC) to one with a low water concentration (LWC). HOW DOES IT HAPPEN? The water in the soil has a weak solution of salts The cell sap has a more concentrated solution Water moves from the soil into the root hair along a water concentration gradient

34 Osmosis

35 Osmosis When water moves into a plant cell by osmosis it increases the pressure inside the cell. The cell walls are sufficiently strong to withstand the pressure. It is this pressure which keeps the cells rigid (maintains their turgor) and provides support. 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). This is why plants needing water ‘droop’ and become limp- WILTED

36 Functions 1. Anchoring the plant
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.

37 2. Absorb essential nutrients
Why? To take up substances to survive. How? Roots have tiny hairs on their surface which increases their surface area to maximise absorption. Many tiny hairs branch off the main root

38 3. Absorb water Why? Water is a raw material for photosynthesis.
A root hair shown under a microscope Root hair cell Root hair Root hair cells also have thin membranes to make it easier for substances to diffuse through into the plant Why? Water is a raw material for photosynthesis. How? Root hairs increase surface area.

39 Transport in Flowering Plants
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. Xylem Tissue Transports water and minerals upwards 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. SQA LO Know the ways which water and food move in the xylem and phloem Interpretation- water and minerals are carried from the roots to the leaves. Water and minerals are carried in tubes called xylem vessels. Food is carried from the leaves to those parts of the plant which need it for growth or energy Or to areas where it is stored. Food is carried in tubes called phloem.

40 Phloem tissue Phloem tissue Carries nutrients,
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.

41 Sugar cane Workbook Activity Leaf Veins are Vascular Bundles.
Vascular bundles are composed of Xylem, Phloem and Fibres which support and protect the xylem and phloem. SQA LO Describe the structure of phloem and xylem and identify other functions of the transport system Interpretation- xylem and phloem are usually found close together in groups called vascular bundles. In stem vascular bundles are round the outside. In root the vascular bundles are in the centre. Vascular bundles also help give the stem support. Xylem cells are dead. The walls of xylem have rings or spirals of a tough substance called lignin. Phloem cells are alive. Phloem contains two kinds of cell: sieve tubes and companion cells. The end walls of sieve tubes have pores. Workbook Activity p 72 Structure of xylem and phloem.

42 Vascular bundles Workbook Activity Vascular Bundles in sugar cane.
Left: cross-section Below: detail of one bundle Use celery stalk. Workbook Activity p 73 Looking at xylem

43 Xylem & phloem in stem Bioviewers Box 78 Workbook Activity
The stem of a flowering plant Workbook Activity p 60 Water transport in plants

44 Position of vascular tissue in the stem
The positions are different in stems compared to roots. In a stem they are round the outside. epidermis xylem phloem

45 Position of vascular tissues in the roots
epidermis xylem phloem Use busy lizzie stem, prestained. Workbook Activity p Structure stem, root In roots they are found in the centre.

46 What Limits photosynthesis?
Light + chlorophyll Ingredients Carbon dioxide + water oxygen + glucose For photosynthesis to happen all the “ingredients” need to be present. If there are inadequate ingredients photosynthesis will stop or slow down. SQA LO Explain what is meant by limiting factors and describe the main factors in the process of photosynthesis Interpretation- a limiting factor is a factor that if in short supply can cut down or limit the rate of photosynthesis. The main limiting factors in photosynthesis are carbon dioxide, light, temperature and water The factor that is in shortest supply will be the one that limits the rate of photosynthesis and is called a “limiting factor”.

47 Factors limiting photosynthesis
Low temperature Shortage of CO2 Shortage of light Lack of chlorophyll  Example: A plant has plenty of water, carbon dioxide and chlorophyll, but it is night. 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…

48 A Light intensity is limiting the rate of reaction A B
B CO2 is limiting the rate of reaction C The difference between the lines is due to different temperatures. p 74 The effect of increasing carbon dioxide p75 The effect of increasing temperature Workbook Activity

49 Quick Quiz 2 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. Guard cells 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

50 Helping plants to grow Plants need mineral salts from the soil for healthy growth. In nature, plants die, decompose and mineral salts return to the ground.  When crops are harvested, the plants are removed, there is no decomposition, and the quality of the soil decreases as less nutrients become available.


52 Manufactured fertilisers are added to the soil to replace those that are lost. This enables healthy crops to grow quickly, but at a cost to the farmer. Questions Why do farmers want to harvest crops quickly? What do fertilisers contain to help plants grow?

53 Signs of Nutrient deficiency in plants
Lack of Nitrogen causes .. Yellowing of leaves. leaves on lower parts of the plant may die Weak stem meaning the plant cannot grow tall.

54 Lack of Potassium causes ….
1. Yellowing of leaves 2. Poor fruit growth.

55 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

56 Lack of Phosphorus causes ….
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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