Topic 2The 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 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: Photosynthesis All living things respire all the time to release energy from their food in a process called: Respiration
Plant survival Light energy carbon dioxide + water glucose + oxygen chlorophyll Plants make their own food, glucose, by photosynthesis. It only happens during the daytime when there is light available. 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). More on the uses for glucose shortly…
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.
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.
Is light needed for photosynthesis? Workbook Problem Solving p 81 Making a starch print Questions: Which parts of the leaf do you think will go blue- black? Why do parts that were not covered contain starch?
Is carbon dioxide needed for photosynthesis? Workbook Problem Solving p 76 Plants and greenhouses 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). CO2 is converted into glucose by photosynthesis.
Plants’ uses of plant glucose Raw material for growth, repair and replacement of damaged parts Used immediately to provide energy source for respiration Glucose 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
Glucose molecule Workbook Activity p 70 Changes in carbohydrate
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. You need to know the plant experiments in detail, explain the different steps, and results, in each one.
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.
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?
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.
Gas Balance Respiration all the time glucose + oxygen carbon dioxide (CO2) + water Photosynthesis daylight only 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 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 Result? A bubble of oxygen gas should form at the top of the test tube as it photosynthesises
Summary of Photosynthesis Workbook Activity p 64-65 Elodea bubbler expt Plants’ waste product- oxygen- is essential for animal life.
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.
A leaf in timeLibrary activity Read through the file and take some short notes to summarise the life of a leaf http://www.portlandpress.com/pp/books/online/leaf/alit_eng.pdf Source: http://www.life.uiuc.edu/plantbio/102/links.html
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)
Internal structure waxy cuticle mesophyll Collect the handout ‘Leaf structure’ and add labels/notes.
Outer layer- upper surface 1.waxy 2. 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…
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.
Workbook Activities p 66-67 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
Outer layer- bottom surface 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.
Stomata- open Workbook 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.
Stomata- closed 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.
General structure Flat leaf blade 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 Stomata Most in lower surface of leaf Gas & water exchange
Leaf veins 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.
Transport systems used for? Workbook Activity p 61 Food transport diagram • 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. Giant redwood trees carry water & nutrients over 100m from the soil
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.
Into the root hair cell Water passes from the soil into root hairs by osmosis 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 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).
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).
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.
2. Absorb essential nutrients 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.
3. Absorb water A root hair shown under a microscope Root hair cell Root hair Why?Water is a raw material for photosynthesis. How? Root hairs increase surface area.
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 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.
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.
Sugar cane Workbook Activity 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.
Vascular bundles Workbook Activity p 73 Looking at xylem Vascular Bundles in sugar cane. Left: cross-section Below: detail of one bundle
Xylem & phloem in stem Workbook Activity p 60 Water transport in plants Bioviewers Box 78 The stem of a flowering plant
Position of vascular tissue in the stem epidermis xylem phloem The positions are different in stems compared to roots. In a stem they are round the outside.
Position of vascular tissues in the roots epidermis Workbook Activity p 68-69 Structure stem, root xylem phloem In roots they are found in the centre.
What Limits photosynthesis? Light + chlorophyll Carbon dioxide + water oxygen + glucose Ingredients • For photosynthesis to happen all the “ingredients” need to be present. If there are inadequate ingredients photosynthesis will stop or slow down. • The factor that is in shortest supply will be the one that limits the rate of photosynthesis and is called a “limitingfactor”.
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…
Rate Light intensity Workbook Activity p 74 The effect of increasing carbon dioxide p75 The effect of increasing temperature ALight intensity is limiting the rate of reaction A B C BCO2 is limiting the rate of reaction CThe difference between the lines is due to different temperatures.
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
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.