World of Plants Sub topic (c) Making food

Food Webs and Plants Animals get their food by eating other living things. Herbivores eat plants. Carnivores eat animals which have eaten plants. Plants have to make their own food. When energy in the form of food passes from a plant to an animal and then on to another animal, it forms a food chain. When we link up all the food chains in an environment we form a food web, e.g.

Plants and Light Plants manufacture their own food in a process called PHOTOSYNTHESIS. When a plant carries out photosynthesis it combines simple substances to make glucose. Glucose can be stored as starch. Photosynthesis is carried out in the leaves of a plant. PHOTOSYNTHESIS (Light) (To build)

Photosynthesis (G) Green plants make their own food which may be stored as starch Green plants convert light energy to chemical energy using chlorophyll The raw materials for photosynthesis are carbon dioxide and water The products of photosynthesis are glucose and oxygen

Photosynthesis Carbon Dioxide +WaterGlucose+Oxygen CO 2 H2OH2OC 6 H 12 O 6 O2O2 Light energy Raw MaterialsProducts

Photosynthesis Photosynthesis CANNOT work without: Carbon dioxide Water Chlorophyll Sunlight If any of the above are in short supply they are said to be “Limiting Factors”.

Starch Test Add leaf to boiling water for 30 seconds This kills the cells - bursts the cell membranes Switch off bunsen burner at this point!

Starch Test Remove leaf and place in a clean test tube Add 10 ml of alcohol Place test tube in beaker of hot water Allow the alcohol to boil for 5 mins The green pigment chlorophyll is removed

Starch Test Pour off alcohol Care! Very hot! Remove leaf with tongs Wash with water. Place leaf carefully onto a dimple tray

Starch Test Carefully add iodine solution over the leaf. Wash the excess off with some water Leave for the colour to develop. Only the green areas turn blue black showing the leaf has made `Starch`

Starch Test Results Leaf from light Leaf from dark Variegated leaf Leaf with CO 2 Leaf without CO 2 black brown black yellow green

Fate of CO 2 in Photosynthesis (C) During photosynthesis CO 2 gas is taken in by plants and made into glucose Glucose provides energy for cellular processes e.g. cell growth, cell division Glucose can also be converted to the storage carbohydrate called starch Or to the structural carbohydrate called cellulose ( makes up the plant cell wall)

Fate of CO 2 in Photosynthesis (C) glucose Structural Carbohydrate (e.g. cellulose in cell walls) Used immediately for energy Stored as starch and converted back when glucose is needed for energy by plant. CO 2

Elodea Bubbler When green plants photosynthesise they produce oxygen. In aquatic plants, this oxygen is given off as bubbles which are easily seen. The Canadian pondweed, Elodea, has large spaces in its stem. When the stem is cut, and the plant is placed in strong light, bubbles of oxygen can be seen coming from the cut end. The number of bubbles produced every minute, i.e. the rate, gives us an idea of how fast the plant is photosynthesising.

Elodea Bubbler Light IntensityNo. of Bubbles per minute Typical Set of Results

Elodea Bubbler

Limiting Factors (C) Photosynthesis depends on carbon dioxide, water, light intensity and temperature. If they are in short supply, they cut down or LIMIT the rate of photosynthesis. “Limiting Factors”.Light, water, carbon dioxide and temperature can act as “Limiting Factors”.

Limiting Factors – light (C) At point X on the graph light intensity is limiting the rate of photosynthesis. At point X - as light intensity increases. the rate of photosynthesis increases At point Y on the graph light intensity is no longer limiting as photosynthesis slows down even though light intensity is still increasing. There must be another factor limiting e.g. CO 2 or temperature X Y

Limiting Factors – CO 2 (C) A B At A CO 2 concentration is the limiting factor as the rate of photosynthesis is increasing as the concentration of CO 2 is increasing At B CO 2 concentration is not the limiting factor as photosynthesis is slowing down even though the concentration of CO 2 is still increasing At B there must be another limiting factor e.g. light intensity or temperature

Limiting Factors –temperature (C) X Z Y At X the rate of photosynthesis is increasing as the enzymes of photosynthesis are working faster At Y the rate of photosynthesis is at its highest because the enzymes of photosynthesis are at their optimum temperature At Z photosynthesis slows down because enzymes are being denatured

Limiting Factors (C) At X the limiting factor is light intensity At Y temperature is limiting At Z CO2 concentration is limiting Y Z

Transport in Plants The transport system of a plant does two jobs. One is to transport materials needed for photosynthesis. Water from roots to leaves The other is to transport nutrients produced by photosynthesis. Sugar from leaves to roots and fruits and all parts of the plant

Water Transport in Plants Water and minerals have to be carried from the roots to the leaves. In the leaves some water is used in photosynthesis. The rest of the water evaporates through pores in the leaf in transpiration

Xylem Tubes, in the stem, called xylem vessels carry the water and minerals. If a plant is cut and placed in red dye, it is easy to see where the xylem vessels are.

Phloem The other job of the plant’s transport system is to carry nutrients (food) from the leaves to every part of the plant. Tubes called the phloem carry the food.

Transport in Plants Stem – Cross Section

Xylem and Phloem Stem – Cross section Cambium

Xylem and Phloem

Structure of the Xylem (C) Xylem cells are dead and have no cell contents – they are hollow tubes The end walls have disintegrated The side walls have become inlaid with a tough waterproof substance called lignin Lignin is arranged in the side walls usually as rings or spirals. A number of these cells laid end to end forms a rigid pipe. This adds considerable support to the plant

Structure of Phloem (C) Phloem cells are living and contain two types of cell Sieve tubes Companion cells In sieve tubes the end walls are perforated (sieve plates) Strands of cytoplasm pass through the pores and allow contact with the next cell. The companion cells lie next to the sieve tubes and have a nucleus sieve plate pores companion cell sieve tube sieve plate cytoplasm

Xylem and Phloem (C) Hollow xylem pipesphloem pipe sieve plate lignin companion cell sieve tube

Leaves Leaves are usually large flat and thin to absorb as much light as possible Leaves take in carbon dioxide from the air. In exchange they give out oxygen produced during photosynthesis. These gases and water vapour must be able to get in and out of a leaf. Leaves have special structures which allow gas exchange. These structures are called stomata

Leaves Not all leaves are large, flat and thin These leaves would lose too much water in a desert Desert plants have small leaves to reduce water loss e.g. spines on a cactus

Stomata Stomata are tiny pores on the surface of a leaf which allow gases in and out. They also allow water vapour to escape. Each pore is a stoma and is surrounded by two guard cells. Stomata can open and close e.g. they open during the day and close at night stoma guard cells stomata

Leaf Surfaces A leaf is very thin and flat. We know it has stomata on its surface. Since a leaf’s job is photosynthesis, there must be reasons for its design. Inside the leaf there are a number of layers, all with different jobs. However, they all help to make photosynthesis as quick and efficient as possible.

Transpiration Transpiration is the loss (evaporation) of water from leaf surfaces. During the day there is a constant flow of water through a plant

External structure of a leaf (C) Leaves are flat thin and broad Leaves don’t overlap so they don’t block sunlight needed for photosynthesis ( leaf mosaic)

Internal structure of leaf (c)

Internal structure of leaf (C)

Cross section of leaf (C)

Cross section of leaf (c) chloroplasts

Function of leaf parts (C) NameFunction Waxy cuticle Waterproof layer – prevents loss of water Upper epidermis Cells that form upper surface of leaf Palisade mesophyll Absorbs light and carries out most of the photosynthesis Chloroplast Cell structure for photosynthesis Spongy mesophyll Exchanges gases between air and leaf cells Moist air space Allows gases to move freely around inside the leaf Stoma Controls gas exchange with the atmosphere Guard cell Controls the size of stoma (opening/closing) Lower epidermis Cells that form lower surface of leaf