NUTRITION . What is nutrition? • It is the uptake of substances by organisms from which energy will be obtained to be used in maintaining life processes (characteristics of living things) Modes of Nutrition • These are principles of obtaining nutrients. • Two modes of nutrition are; • a) Autotrophic- whereby organisms (plants) build up all their food i.e. making organic molecules from simple inorganic substances. • Auto- means self and trophos means feeding. Modes of Nutrition • Heterotrophic- whereby organisms (animals) use ready made organic substances as their source of food. These organic substances are originally from autotrophs • Hetero means different or other. Why do organisms need nutrition? • • • • give organisms energy For growth (building cells and tissues repairing worn out/ damaged tissue (healing wound) maintaing life/carry out life processes (breathing) PLANT (AUTOTROPHIC) NUTRITION • Why are plants referred to as producers? • Plants able to make (produce) their own food through the process of photosynthesis Photosynthesis • can be defined as; • The process by which green plants make their own food using water and carbon dioxide in the presence of sunlight. • The process by which green plants fix complex organic substances such as carbohydrates from inorganic substances such as carbon dioxide and water. Raw materials needed for photosynthesis • • • • Carbon dioxide Water Sunlight Chlorophyll How do plants obtain these raw materials? • Carbon dioxide - diffuses through the stomata found on leaves and some stems. • Water – it is absorbed from the soil by the root hair cells through the process of osmosis. Water moves between the cell walls through to the xylem tissues which is responsible of transporting water and dissolved mineral salts. • Sunlight – it is trapped by the green pigment called chlorophyll • Chlorophyll – is a green pigment found mostly in leaves and is made by chloroplasts. • The process of photosynthesis can be summarized through the following equations; • Word equation; Sunlight • Carbon dioxide + Water → chlorophyll → Carbohydrates + Oxygen • Chemical symbol equation; Sunlight • 6CO2 + 6H2O→ chlorophyll→ C6H12O6 + 6O2 The importance of photosynthesis • Almost all forms of life depend on the chemical energy found in carbohydrates produced by photosynthesis. • The oxygen produced by photosynthesis is essential for the process of respiration • The process of photosynthesis uses the atmospheric carbon dioxide thus maintaining an ecological balance and minimizes the green house effect. NB: Although photosynthesis occurs mainly in the leaves, any part of the plant that contains chlorophyll will also photosynthesize. The Leaf Structure • Most leaves are thin thus carbon dioxide can easily diffuse across the short distances to reach the inner cells • Intercellular air spaces provide an easy passage for diffusion of gases. • There are many stomata on the lower epidermis to allow for exchange CO2 & O2 and minimize loss of water by transpiration • There are more chloroplasts on the upper cells (palisade) than on the lower cells (spongy) • The branching network of veins (xylem & phloem) provides transport system for good supply of water to the cells and carrying away of nutrients from the cells. . Leaf Structure FUNTIONS OF THE PARTS • Cuticle- this is a waxy layer on the upper epidermis which prevents water loss by transpiration • Epidermis- found on the upper and lower surfaces of the leaf. It helps to keep the leaf in shape and protects the inner parts of the leaf form micro-organisms. Also reduces transpiration. FUNTIONS OF THE PARTS • Mesophyll – is the tissue between the epidermal tissues. a) Palisade mesophyll tissue – Column-shaped (or elongated) cells which contain lots of chloroplasts to ensure maximum absorption of light. Is the site for photosynthesis. b) Spongy mesophyll tissue – irregularly shaped cells which fit loosely to allow for easy diffusion of gases. FUNTIONS OF THE PARTS • Vascular bundle – contains the mains transport tissues a) Xylem vessels – transport water and mineral salts from the roots to the leaves through the transpiration pull. b) Phloem vessels – transports manufactured food to growing parts of the part. • Guard cells – in most plants there are mainly on the lower epidermis. They surround small openings called stomata through which gases diffuse in and out. The fate of glucose following the process of photosynthesis Sunlight absorbed by Chlorophyll to photolyse water CO2 + H2O CO2 + H2 O2 = C6H12O6 (GLUCOSE) (released as a by product) The fate of glucose following the process of photosynthesis . C6 H12 O6 (Glucose) Proteins used to make enzymes, cytoplasm etc Sucrose used for respiration Converted to Oil & Fats used to make cell membrane Cellulose used to make cell wall Testing Green leaf for starch Background information • The leaf manufactures carbohydrates through the process called photosynthesis. First, plants manufacture sugars which are later converted to starch for storage in the cells to find out if photosynthesis has taken place we test the leaf starch. Apparatus • • • • • • • • 2 Beakers test tube burner leaf white tile ethanol water testing reagent- iodine solution Procedure • Step 1 • Boil the leaf for 3 minutes in order to break open the cells. This also helps to kill the cell cytoplasm and make the leaf permeable to iodine solution. Procedure • Step 2 • Boil the leaf in ethanol (alcohol) for 2 minutes to remove the chlorophyll. • Caution; ethanol is flammable; therefore do not heat it directly. Procedure • Step 3 • Put the leaf in warm water to soften it. Ethanol makes the leaf hard and brittle. Procedure • Step 4 • Place the leaf on a white tile and add 3 drops of iodine solution. SUMMARY-PROCEDURE Results • If starch is present the decolourised leaf will turn blueblack and if there is no starch it will just stain reddish brown.
