Untitled Flashcards Set

F: Plants and environment:  unit 3  

Factors affecting plant growth  

Two types of factors: 

1. Abiotic factor  

2. Biotic factors 

Abiotic factors: these are none living factors of the environment, these factors include:(human activities) 

1. Light intensity  

2. Temperature  

3. Soil ph. 

4. Aeration of soil- oxygen present in the soil 

5. Water availability in soil  

6. Minerals ions present in the soil  

 Biotic factors = these are the living factors of the environment (human activities)  

Biotic factors include:  

1. trampling of the soil by humans / animals walking 

2.  Habitat destruction by humans such as removing trees for growing crops  

3. Pollution: air/ land/ soil pollution by human activities  

4. Use of pesticides on soil to kill pests feeding Apon the crops  

5. Over hunting of animals / fish for human benefits  

6.  Monoculture: removing variety of different tree species and replacing it with only one type of crop plants, e.g.: wheat plants  

Effects of abiotic factors:  

1.  Light intensity – light is needed for the opening of stomata to allow co2 to diffuse into the leaf for photosynthesis. Light is absorbed by chlorophyll to produce sugar in photosynthesis. 6CO2 + 6H2O → C6H12O6 + 6O2  

Main points for exam: 

1.  Sunny areas: higher rate of photosynthesis and plants grow larger and faster  

2. Shaded areas: lower rate of photosynthesis and plants are smaller and grow slowly 

3.  In summer more sunlight and longer day length therefore higher rate of photosynthesis and plants grow faster  

4. In autumn and winter there is less sunlight and shorter days therefore a lower rate of photosynthesis and plants grow slowly.  

2^nd factor: temperature: 

1. Photosynthesis, which produces sugars in plants, is an enzyme catalyzed reaction.  

2. Enzymes are affected by temperature so optimum temperature, e.g.: 25 *c means plants growth is highest  

3. Very low temperature will slow down the plant growth and very high temperature will denature enzymes in plants, so plants do not grow either. 

4. (important) Very low temperatures such as 0*c is damaging to plant growth as, ice crystals in plant cell surface membrane destroying plant cells, there for death of plants. 

Tuesday 3^rd dec: 

When the temperature is high, the rate of respiration of plants is also high, this also means sugars produced in photosynthesis is used up in respiration, so less sugars are available for plants to grow, so sometimes very high temperature is inhabiting plant growth.  

Please note photosynthesis produces sugar, but respiration uses sugar to produce energy as ATP is needed for cells metabolic processes.  

Plants photosynthesize in the daytime but respire day and night 

Respiration requires sugar to be oxidized so sugar made in photosynthesis is used up  

3: water availability: 

1. Water is needed for various purposes in plants that is needed for growth  

2. Water is needed as a solvent to dissolve range of inorganic ions like nitrates and phosphates and dissolved sugar 

3.  These ions and sugars are then transported to different parts of a plant to allow growth to take place.  

4. Water is needed as a transport medium to transport ions and sugars needed for growth 

5.  Water is an important reactant in photosynthesis 

6.  Water combines with carbon dioxide to produce glucose in photosynthesis 

7. Water is needed to maintain turgity in plant cells, so the leaves are spread out to absorb more sunlight and the stem of the plant stands upright against the force of gravity.  

8. Water provides an aqueous medium in which enzymes and substrates react to gather to make products in cell cytoplasm. 

9. When the sunlight falls on the leaves water molecules evaporate as water vapor, this is known as transpiration, and this transpiration pulls more water molecules from the root to the leaves to replace lost water molecules  

10.  When the water molecules evaporate as water vapor, this cools some plants that grow in hot and humid conditions like the tropical rainforest. 

4: aeration of soil: 

1. This is known as oxygen concentration present in the soil pores. 

2. Oxygen is needed by the plant roots to respire aerobically and release energy as apt for active uptake for salt ions. 

3. Oxygen is needed for the aerobic respiration of plant root cells and if oxygen is not available then root cells respire anaerobically producing ethanol which is toxic to plants and kills plants.  

4. Oxygen is needed by plant cells to respire aerobically releasing apt that is used to make chemicals such as Tannins and terpenes, which prevent growth of the plant's pathogens, so plants remain healthy and free of infection. 

5. Oxygen is needed by the soil micro-organisms to respire aerobically, and they help to recycle nutrients in the soil. Plants can use these nutrients to grow  

5: Ph of soil: 

1. Plants like slightly acidic Ph = 6.8, but most plants grow well withithin the ph. range of 4.5 to 7.5. 

2. When the Ph is optimum, plant proteins and enzymes are not denatured and the rate of photosynthesis is the highest producing more sugars, so plants grow more. 

3. Very acidic or very alkaline ph. denatures the plant proteins and enzymes, and plant growth is inhabited 

6: nutrients of the soil: 

1.  These are the range of inorganic ions needed for plant growth to make large molecules such as proteins; lipids, starch, DNA and ATP. 

2. All these molecules are needed for plant to grow bigger and faster for example, nitrates needed for protein synthesis and amino acid synthesis  

3. Phosphates are needed for DNA, RNA and ATP synthesis. 

4. Sulphates are needed for amino acid synthesis  

5. Magnesium is needed for chlorophyll synthesis.  

Biotic factors affecting plant growth: 

These are the factors affecting plant growth: 

 Trampling: 

1.  When humans and animals walk in the region with plants, the soil structure gets damaged, and this dislodges roots and stems of plants, so plant growth is affected. 

2. As plants are not able to absorb nutrients from the soil, they cannot synthesize large molecules like DNA, RNA and carbohydrates proteins and lipids which are needed are needed for plant growth.  

3. When the region is not trampled, the plants' roots and stems are not dislodged, meaning they can absorb from the soil and grow taller and faster.  

Summery points: 

4.  trampled region = low plant diversity  

5. Untrampled region = high plant diversity  

2: human activity  

1. Such as deforestation felling trees, to clear land for the agricultural purposes, 

2. Eg: Brazilian rainforest which has very high plant diversity is cleared to crop plants  eg: wheat for human benefits  

3.  Trees removed, so fewer producers photosynthesize and produce sugars.  

4.  So, herbivore animals which feed Apon the producers eg plants will die out or move away. and therefore, carnivore animals which feed Apon herbivore animals also move away or die out  

5.  So, the food chain in the food web is affected and this effects the ecosystem stability  

6. This overall reduces biodiversity of the ecosystem  

3: pollution: 

1.  Human activity such as combustion of fossil fuel (coal/ oil/ gas) s releases harmful gasses to the environment 

2. These gasses include carbon dioxide of oxides of nitrogen 

3.  These gasses dissolve in rainwater to form carbonic acid, sulfuric acid, and nitric acid  

4. This forms acid rain where the ph. of rainwater falls below 6.5. 

5. The acid rain destroys leaves, plants, shrubs and causes blackening of the leaves. 

6.  This results in reduction in surface area of leaves and less photosynthesis so less sugar for plant growth. 

4: chemicals by farmers to increase plant productivity 

1. Farmers use two types of chemicals to increase plant growth  

•  Farmers use pesticides to kill pests which destroys crop plants by eating plant tissue or by absorbing sugars made in photosynthesis  eg: green flies eat crop plants  

1. However, these pesticides are nonspecific which means they also kill non pest species for example bumble bees which are needed for crop pollution, this means crops have lower genetic diversity.  

2. Pesticides also accumulate in the environment as they are not broken down naturally by sunlight or microorganisms in the soil. 

3.  Pesticides can enter the food chain / food web and humans can consume it with unknown harmful effects e.g.: DDT pesticides known to have caused cancer in human females and have been banned worldwide.  

4. Pests can also develop resistance against the pesticides after repeated use.  

5. B: farmers use fertilizers (NPK) to promote crop growth,  

6. Fertilizers add nutrients into the soil which are absorbed by plants to produce macro molecules however extra fertilizers are running off soil and gets deposited into the water bodies, e.g.: lakes ponds and rivers and this promotes algal bloom (green plants on surface,)  

7.  This process is known as eutrophication, which reduces oxygen supply in the water, and this causes freshwater invertebrate animals to die e.g.: fish  

Monoculture: 

1.  This is a practice and in this process the farmer removes a variety of different plants from the field and replaces this with only one type of cropped plant e.g.: wheat plant. 

2.  This is done so that the prop plant does not have any competition for resources and grows larger and faster. However, the monoculture replaces high plant biodiversity with low plant biodiversity  

3.  And disrupts soil structure and eventually lowers plant growth.