Presentation on theme: "Topic 2 The World of Plants Standard Grade Biology."— Presentation transcript:
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 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: Photosynthesis All living things respire all the time to release energy from their food in a process called: Respiration
Plant survival 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). Raw materialsProducts carbon dioxide + water glucose + oxygen chlorophyll More on the uses for glucose shortly…
Is light needed for photosynthesis? 1.Take a de-starched geranium plant (24h in dark). 2.Cover part of a leaf with some tin foil (this prevents light getting through). 3.Leave the plant in sunlight for a few hours. 4.Test the leaf for starch.
Is carbon dioxide needed for photosynthesis? 1.Take a de-starched geranium plant 2.Enclose it in a plastic bag with a chemical that absorbs carbon dioxide. (e.g. soda lime or sodium hydroxide pellets). 3.Leave the plant in sunlight for a couple of hours. 4.Test the leaf for starch.
Questions: 1.Which parts of the leaf do you think will go blue- black? 2.Why do parts that were not covered contain starch? Is light needed for photosynthesis? Workbook Problem Solving p 81 Making a starch print
Is carbon dioxide needed for photosynthesis? Questions : 1.Does the leaf contain starch? Why/ why not? 2.Has the plant carried out photosynthesis? 3.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 CO 2 is converted into glucose by photosynthesis.
Mans’ uses of plant glucose
Plants’ uses of plant glucose Glucose 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 cellulose, the main structural material in cell walls Raw material for growth, repair and replacement of damaged parts Energy stored as starch (in leaves, seeds, roots and tubers) To make fats & oils (energy stored in seeds) Energy stored as sucrose (in fruit)
Glucose molecule Workbook Activity p 70 Changes in carbohydrate
Activity – Testing a plant for sugar 1.Put a piece of raw onion in a pestle and mortar. 2.Grind it with a little sand and 10cm 3 of water. 3.Filter the liquid into a test tube 4.Heat the liquid with 10 drops Benedict’s solution in a water bath a)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 1.Dip a leaf into boiling water for about a minute (to soften it). 2.Turn off the Bunsen burner. 3.Put the leaf into a test-tube of ethanol (to remove chlorophyll). 4.Stand the test-tube in a beaker of hot water for about 10 minutes. 5.Wash the leaf in cold water. 6.Spread the leaf out flat on a petri dish and cover it with iodine solution (tests for starch). 7.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… Where do the extra 250kg come from? Explain your answer as fully and scientifically as you can. 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.
Gas Balance During the day: Oxygen released by photosynthesis is greater than the amount of oxygen used up in respiration. CO 2 used in photosynthesis is greater than the amount of CO 2 produced by respiration. glucose + oxygen carbon dioxide (CO 2 ) + water carbon dioxide + water glucose + oxygen all the time daylight only
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 Elodea bubbler expt Plants’ waste product- oxygen- is essential for animal life.
Quick Quiz 1 1. What does a plant need for photosynthesis? 2. What does a leaf produce during photosynthesis? 3. What is chlorophyll? 4. How do the leaves obtain water? 5. How does the plant obtain carbon dioxide? 6. List 3 uses of the glucose produced by photosynthesis? 7. Name the storage form of carbohydrate in a leaf. Carbon dioxide, water, chlorophyll, light. Oxygen, glucose A green pigment which absorbs the sun’s energy Through the roots (and xylem tubes by osmosis From the air (through stomata) Cellulose (structural), starch (storage), energy Starch.
A leaf in time Library activity Source: Read through the file and take some short notes to summarise the life of a leaf alit_eng.pdf
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 Collect the handout ‘Leaf structure’ and add labels/notes. mesophyll waxy cuticle
Outer layer- upper surface 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… 1.waxy 2.
The palisade layer contains cells with lots of chloroplasts. The spongy layer (spongy mesophyll) contains rounded cells with many air spaces allowing CO 2 to circulate and reach the palisade cells, while O 2 leaves. Hence this is where most photosynthesis occurs. Chloroplasts contain chlorophyll which is the chemical which absorbs the sun’s light energy. mesophyll
Workbook Activities p 66-67Leaf surface and thickness p67Leaf layer cards- matching Problem Solving p78 How many stomata? p79 Water content and dry weight. p85 Use of cobalt choride paper BioviewersBox 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 CO 2 diffuse in. Water vapour and oxygen (O 2 ) move out.
Stomata- open 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 p 62 Leaf surfaces
Stomata- closed 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. Workbook ActivityPS p63 stomata behaviour p82 & 83 Leaf balance
General structure Vast network of veins supplies all parts of the plant with essential substances Structural support Flat leaf blade Has large surface area Absorbs as much sunlight & CO 2 as possible Thin CO 2, reaches inner cells easily Stomata Most in lower surface of leaf Gas & water exchange
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
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. Giant redwood trees carry water & nutrients over 100m from the soil Workbook Activity p 61 Food transport diagram
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 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 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).
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).
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. Functions 1. Anchoring the plant
Many tiny hairs branch off the main root 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.
A root hair shown under a microscope Root hair cell Root hair 3. Absorb water 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 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.
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 Vascular bundles are composed of Xylem, Phloem and Fibres which support and protect the xylem and phloem. Leaf Veins are Vascular Bundles. Workbook Activity p 72 Structure of 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 BioviewersBox 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 xylem phloem Workbook Activity p Structure stem, root In roots they are found in the centre.
What Limits photosynthesis? For photosynthesis to happen all the “ingredients” need to be present. If there are inadequate ingredients photosynthesis will stop or slow down. Light + chlorophyll Ingredients Carbon dioxide + water oxygen + glucose The factor that is in shortest supply will be the one that limits the rate of photosynthesis and is called a “ limiting factor ”.
Factors limiting photosynthesis Low temperature Shortage of CO 2 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 AB C A Light intensity is limiting the rate of reaction B CO 2 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
Quick Quiz 2 2. Give 2 structural features of a leaf that make it a good design for photosynthesis. 3. Why do you think that the palisade cells are near the surface of the leaf? 4. Name the cells that surround the stomatal openings. 5. The spongy mesophyll cells are loosely arranged. Explain the significance of this. 6. Which 3 factors limit the rate of photosynthesis? 1. How is glucose carried from the leaves to every part of the plant? Transported in phloem tubes (water in xylem) Large surface area, thin, stomata, veins To absorb as much sunlight as possible in chloroplasts Guard cells Large spaces between cells allow gases to diffuse quickly 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.
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 1.Why do farmers want to harvest crops quickly? 2.What do fertilisers contain to help plants grow?
Signs of Nutrient deficiency in plants Lack of Nitrogen causes.. 1. Yellowing of leaves. 2. leaves on lower parts of the plant may die 3. Weak stem meaning the plant cannot grow tall.
Lack of Potassium causes …. 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 bottom of a plant Leaf from the top of a plant
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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