biology term 2

saprophytes

feed on dead organic material. example decomposers that feed on dead heterotrophs and autotrophs

limiting factor - availability of water

the availibility of water varies in the environment. if the soil is dry, water maybe the limiting factor on photosynthesis

Dark reaction

the second reaction takes place without both light and chlorophyll and is called light independant or dark reaction stage in this stage the hydrogen which was realeased from from water in the light reaction is used to reduce carbon dioxide. hydrogen then combines with carbon dioxide to make glucose (C6 H12 O6) this stage of photosynthesis can be carried out without sunlight and can happen when it is dark.

heterotrophs

feed on other organisms. example consumers that feed on plants and other animals

Light reaction

photosynthesis takes place in 2 stages the first stage needs light which is absorbed by the chlorophyll and is called the light reaction. the light energy absorbed by the chlorophyll is used to split water molecules into hydrogen ygen. oxygen is a waste product and diffuses out of the leaf. the pigment of chlrorophyll is green so that it traps the light. fromula for the light reaction H2O LIGHT H+O2 light splitsH2O.

photosynthesis

the ability to create food using light. types of organisms that can photosyntisize are autotrophs. autotrophs are self feeding organisms. plants are autotrophs since they can use sunlight to create food and energy via the process of photosynthesis. equation for photosynthesis 6CO2 + 6H2O sunlight and chlorophyll C6H12O6 + 6O2.

limiting factor - light intensity

the amount if light in the environment varies greatly between night and day. light is usually the limting factor from dusk to dawn.

limiting factor - carbon dioxide concentration

the concentration of carbon dioxide is relatively low in the atmosphere. so carbon dioxide is usually the limiting factor when temperature and light levels are high. commercial grwoers who grow their crops in large green houses often pum in extra carbon dioxide to increase the rate of photosynthesis in the crops

the fate of glucose

the fate of glucose means what would happen to glucose after it has been produced in photosynthesis. glucose could be used in several ways 1.) used in respiration by leaf cells 2.) it is converted to starch and stored in leaf cells 3.) converted to sucrose and transported to other parts of the plant, mainly storage organs and growing parts where it is converted to [1.) glucose and used in respiration. 2.) cellulose and used to make cell walls, in growing parts of the plant. 3.)converted back to starch and stored in the storage organs. 4.) converted to ammino acids and proteins with the addition of nitrogen and sulphur used for growth. 5.) converted into lipids and stored.] 1.) glucoes is produced in photosynthesis. 2.) glucose cannot be transported to other parts of the plant in the phloem tube. 3.) glucose is too reactive to move is phloem tubes. 4.) it has to be converted to sucrose to move. NOTE starch is a polymer of glucose (one starch is a glucose, more than one glucose is starch) glucose is a monomer of starch

products of photosynthesis

the glucose produced in photosynthesis is used in several ways : it is broken down during respiration to release energy so the plant can carry out all the processes of life. it is converted to starch and stored in the leaf to be used at night when the plant is not photosynthesising. it is converted to sucrose and transported to other parts of the plant it can then be converted to other carbohydrates, lipids and proteins and used for growth, or it can be converted to starch and stored, as in potatoes.

limiting factor - temperature

the rate of reaction increases as temperature increases. with heat, the molecules move about and come together faster. photosynthesis also involves a series of enzyme - catalysed reactions. enzymes have an optimum temperature at which they work best, so this will also affect the rate of reaction. temperature is often a limiting factor on the rate of photosynthesis in cool seasons in temperate regions.

autotrophs

self feeders. example plants that make their own food

etiolation

if the plant cannon get sunlight for example it is shaded by a rock or blocked by another plant, it cannot photosynthesise. without photosynthesis the plant cannot make food. but that does not mean it cannot continue to grow. for a short while it can continue to grow using the food stored within the plant to grow and lengthen. this gives it a chance to get some leaves into the sunlight and so start to photosynthesise again. the form of growth that a plant shows when it is out of the light is different from normal. all the energy is used to make long thin cells. so the stem becomes elongated and thin, and leaves are kept very small. the stems and leaves are also pale yellow as no chlorophyll is made. this form of growth is called etiolaton. if it does not reach light quickly it would run out of food reserves and die.

stomata and guard cells

in intervals along the epidermis, there are stomata. each stomata is an opening or pore surrounded by a pair of crescent shaped guard cells which can change shape. when the guard cells change shape the pore in between the opens and closes. the opening or closing or the guard cells depends on LIGHT INTENSITY and whether the guard cells gain or lose water. if they gain water the internal pressure in the cell increases. since they are thicken along the inner wall. both cells bend so that they curve away from each other. this widens the space between them which allows carbon dioxide to enter easily and facilitate the proess of photosynthesis. the stomata allows the exchange of gases for photosynthesis, transpiration and respiration

adaptations of the leaf for photosynthesis

leaves are adapted to carry out photosynthesis. external adaptations: they are generally broad and flat with a large surface area to absorb to absorb alot of light and carbon dioxide, they lie 90 degrees to the sunlight and are spaced around the stem to catch as much sunlight as possible, the leaves are thin sothat it allows sunlight to reach all cells rapidly. stomata (small holes) are present in the lower epidermis to allow gases to get in and out easily (one hole is a stoma, stomata is plural). air spaces around the cells in the lower half of the leaf allow carbon dioxide to get to the chloroplast as quickly as possible. palisade cell - chloroplast are most numerous in cells in the palisade layer, which is in the top part of the leaf, closest to sunlight. xylem vessels transport water to the leaf cells. phloem sieve tubes carry away the food made in the leaf celss to other parts of the plant. a waxy cuticle prevents water loss from both surfaces of the leaf and is transparent to let light through

limiting factors in photosynthesis

photosynthesis is a chemical reaction and the rate at which a reaction can happen depends on how fast the chemicals that are reacting can get together. in photosynthesis a plant requires water carbon dioxide and light if anyone of these are in short supply, the rate of reaction would slow down. for example a plant may have sufficient water and carbon dioxide but not enough sun light for photosynthesis to take place at its maximum rate. light is then said to be a limitng factor since the rate of photosynthesis is limited by the amount of sunlight. the reacttion would take place at a rate that is limited by the factor which is at its least favourable value (light in this example). water, carbon dioxide and light maybe limiting factors for photosynthesis at different times . limiting factors which affect photosynthesis are : temperature, light intensity, carbon dioxide concentration availability of water.