Chapter 5 Obtaining Energy and Nutrients for Life
WEEK 6: Obtaining Nutrients LEARNING OUTCOMES By the end of this week, you should be able to explain: Biochemical processes including photosynthesis and cellular respiration in terms of inputs and outputs. Obtaining nutrients: organic and inorganic requirements; autotrophs; heterotrophs. Obtaining energy: inputs and outputs of photosynthesis; structural features of photosynthetic organisms. Processing nutrients: features of effective systems in heterotrophs; examples of systems in different animals.
LESSON 1: Heterotrophs, autotrophs and photosynthesis LEARNING OUTCOMES By the end of this lesson, you should be able to: Define ‘autotroph’ and ‘heterotroph’. Distinguish between heterotrophs and autotrophs in terms of nutrient requirements for life. Summarise the process of photosynthesis in a word equation and chemical equation. Identify structural features of photosynthetic organisms that facilitate their ability to photosynthesise.
Active and Passive What do the terms mean? Watch the clip.... Is the whale shark an active feeder or a passive feeder?
Heterotrophs Actively obtain the energy they need for life by feeding on organic matter found in their surroundings (food!) They then use this organic matter to build and repair their cells. Give some examples... What structural, physiological and behavioural adaptations do heterotrophs have to help them obtain their food?
Autotrophs Organisms that just take up (absorb) the energy they need from their surroundings. They build organic matter from simple inorganic matter taken up from the air, soil or water. Give some examples.....
Carnivorous Plants Carnivorous plants still need water and sunlight like other green plants to make food/energy (glucose) but they get their mineral nutrients from trapping and consuming animals. Carnivorous plants are adapted to grow in places where the soil is thin or lacking nutrients, especially nitrogen, such as acidic bogs and rock outcroppings.
Photosynthesis Plants, algae and some protists can make sugars by photosynthesis. Sunlight energy is converted into chemical energy (in the form of glucose) in the chloroplasts found in the cytosol of cells.
Plants use the energy from the sun to make molecules such as glucose, starch and proteins. These molecules can then be used for food for the plant, but also for animals like us. A waste product of the process is oxygen, which is released into the atmosphere.
The Importance The importance of photosynthesis is in the conversion of unusable sunlight energy into usable chemical energy (glucose). It is one of the most important biochemical processes, since nearly all life on Earth either directly or indirectly depends on it as a source of energy.
The Equation Word equation: Balanced chemical symbol equation: light chlorophyll light chlorophyll carbon dioxide+ waterglucose+ oxygen 6CO 2 + 6H 2 OC 6 H 12 O 6 + 6O 2
Or: six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen.
Plants absorb water through their roots, and carbon dioxide through their leaves. Some glucose is used for respiration, while some is converted into insoluble starch for storage. The stored starch can later be turned back into glucose and used in respiration.
Testing a green leaf for starch Will a plant that has been kept in a dark cupboard for a few days contain starch in its leaves?
Structure of the Leaf PPhotosynthesis takes place mainly in the cells of the leaves. LLeaves are well adapted for photosynthesis – its structure is well suited to its function. LLeaves are made up of four main layers: UUpper epidermis PPalisade layer SSpongy layer LLower epidermis Mesophyll layer
Epidermis Single layer of cells on the upper and lower surfaces of the leaf. Helps to keep the leaf’s shape. Has closely fitting cells: Reduces evaporation from the leaf Prevents bacteria and fungi from getting in Thin waxy layer covering epidermis called the cuticle – helps to reduce water loss further. Have stomata. In woody stems, the epidermis is bark.
Stomata Singular: stoma Structures in the leaf epidermis. Consists of a pair of guard cells, surrounding an opening called the stomatal pore. The stomata can open and close by changes in the turgor and shape of the guard cells. In some plants they are located on the lower epidermis only, others have stomata on both sides of the leaf.
How Do Stomata Work? Generally, they open during daylight hours (whilst photosynthesis is taking place) and close during the night. Why? What do plants need to photosynthesise? During the day they are open to allow carbon dioxide to diffuse into the leaf (and oxygen out) so photosynthesis can take place.
Mesophyll Tissue between the upper and lower epidermis. Consists of two layers (see diagram). PALISADE CELLS: Function – to make food by photosynthesis. Hence, they have lots of SPONGY MESOPHYLL CELLS Vary in shape, and fit loosely together. Many air spaces between them. chloroplasts.
Air Spaces Whilst photosynthesis is taking place, the air spaces in the mesophyll layer fill with carbon dioxide as it enters the leaf, and oxygen as it leaves the leaf.
Veins (vascular bundles) Xylem vessels carriy water needed for photosynthesis to the mesophyll cells. The mesophyll cells take in water through osmosis. Branching network – no cell is far away from a water supply. Sugars made in mesophyll cells are passed to the phloem cells – carry sugar away from the leaf to the stem.