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Plant Nutrition and Photosynthesis

Plants are living organisms that need food in order to stay alive. The way they obtain their nutrients though, is totally different from that of animals.

Plant produces the majority of their nutrients by themselves with the aid of merely 2 raw materials; water and carbon dioxide.
The leaf of a plant is taken as its kitchen. It is where food is manufactured and transported round the plant body.

Parts of the leaf:

1. Upper Epidermis: This is a layer of cells that envelop the leaf and protect it, it is enclosed by a layer of wax known as the cuticle.
2. Mesophyll Layer:
The mesopyll layer of the leaf is further dived into:
Palisade Mesophyll: a layer of palisade cells takes care of the majority of the function of photosynthesis in plants
•Spongy Mesophyll: a layer of spongy cells under the palisade layer which also takes part in photosynthesis and store nutrients.
3. The Vascular Bundles: These are a group of phloem and xylem vessels that transport water and minerals to and from the leaves.
3. Lower Epidermis: This is related to the upper epidermis, only that it contains a unique type of cells known as the guard cells.
Guard cells are a special type of cells that regulate the passage of carbon dioxide into the cell and the passage of oxygen out of the cell by opening and closing of the stomata.
The stomata are a hole in the leaf through which gases pass through. Therefore, guard cells are responsible for gaseous exchange in plants.

Photosynthesis:

The term photosynthesis means “producing with light”. It is the process by which plants manufacture useful glucose out of the raw materials of water and carbon dioxide, with the help of the light energy from the sun.
Water is vital for photosynthesis; it is obtained from the soil by the roots and transported up the stem to the leaves where it is put into effective use.
Carbon dioxide, like water is necessary for photosynthesis to occur. It travels into the leaf from the air through the process of diffusion, via the stomata which are minute holes in the leaf.
As soon as carbon dioxide and water are available in the leaf, the next condition for photosynthesis that is needed and that is light.
The two cells known as palisade cells, the rectangular one and spongy mesophyl cell -the circular one, are the cells where photosynthesis takes place.
They a structure known as chloroplasts which contain a green pigment known as chlorophyll which functions at trapping sunlight to be used as energy for the photosynthetic reaction. A large number of chloroplasts is needed for photosynthesis to occur.
How photosynthesis takes place:
•Carbon dioxide and water go into the cell
•The cell traps light energy with the use of chloroplasts
•The energy is utilized to split water (H2O) into hydrogen and oxygen
•The oxygen is expelled outside the leaf to the atmosphere as a waste product
•The hydrogen reacts with carbon dioxide to form glucose.
Carbon Dioxide Supply:
The carbon dioxide travels to the leaf from the atmosphere by diffusion through tiny holes in the leaf known as the stomata.
Carbon dioxide is not available in a high concentration in air, but when compared to its concentration inside the leaf, it is more concentrated in the air.
This is because the cells inside the leaf are constantly photosynthesizing during the day time converting the carbon dioxide into the glucose rapidly, therefore the concentration of it inside the leaf lessens, producing a concentration gradient for diffusion from the atmosphere to the leaf.
Water Supply:
The water for photosynthesis is absorbed by the roots of the plants and then transported upwards via a hollow tube known as the xylem vessel till it arrives at the leaf where photosynthesis occurs; it passes through the leaf through holes in the xylem.
Excess water leaves the cell via the stomata; through the process known as “transpiration”
Sunlight Supply:
The leaves are always exposed to sunlight at daytime. The sun penetrates the transparent layers on the leaf till it gets to the mesophyll layer, where photosynthesis occurs.
Palisade cells are closer to the surface of the leaf than the spongy cells, so they receive more of the light and undergo more photosynthesis.
Factors Needed For Photosynthesis:
•Water
•Carbon Dioxide
•Light
Factors Affecting The Rate Of Photosynthesis:
•Amount of water: the rate of photosynthesis increases as water increases
•Concentration of carbon dioxide: the rate of photosynthesis increases as CO2 increases
•Light intensity: the rate of photosynthesis increases as light increases

Plants at night:

At night, the plant goes through a lot of processes to convert the stored starch into numerous useful nutrients such as:
•Sugars for respiration
•Cellulose and proteins for producing cells
•Vitamins to assist in energy action
•Fats as a long term storage material
•The rest of the starch is temporarily stored.

Mechanism of Guard Cells:

At daytime, the guard cells open the stomata to permit gaseous exchange, which takes place following the processes below:
•Sunlight increases the potassium concentration in the vacuoles of the guard cells, the water latency decreases producing a gradient between the guard cells and the surrounding epidermal cells,
•Water travels through the process of osmosis into the guard cells from the epidermal cells,
•The water increases the pressure inside the guard cells,
•The cell wall adjoining the stomata is thicker and less stretchable then the cell wall on the other side,
•The pressure expand the whole cell apart from the inner cell wall adjoining the stomata by forming a curve and a pore between the two guard cells,
•The stoma opens.
At night on the other hand, the mechanism is reverse:
•Potassium level lessens in the vacuole of the guard cells,
•Water potential rises in the cell and water diffuses out of it,
•The guard cells uncurl up due to low pressure closing the stoma.
Mineral Requirements:
The plant is as well in need for mineral ions to be in charge of chemical activities, grow, and manufacture materials. The major important minerals are:
•Mg+2 (Magnesium ions): They are necessary for the production of the green pigment known as chlorophyll. Deficiency of it leads to lack of photosynthesis and wilting of the leaves,
•Nitrates: these are the sources of nitrogen; they are needed to make amino acids and proteins by combining with glucose. Deficiency of it leads to deformation of the plant structure making it small and weak.
The two mineral ions are absorbed from the soil.
Fertilisers:
Occasionally, the soil is deficient of the mineral ions necessary; this issue can be resolved by the addition of fertilizers to the soil. Fertilizers are chemical compounds rich in the mineral ions required by the plants.
They assist the plants to grow faster, increase in size and become greener; they merely make them healthier and increase the crop yield. But there are disadvantages of fertilizers, like:
•Excess minerals and chemical can pass into a nearby river polluting it and creating a layer of green algae on the surface of it, resulting to the lack of light in the river, thereby inhibiting the aqua plants photosynthesizing.
•When living organisms in the river or Lake Die, decomposers like bacteria multiply and decay, respire with the use of oxygen. Eutrophication occurs in the end.

The green House

A green house is a place sheltered by transparent polythene. In green houses, the restraining factors of photosynthesis are eradicated, and the plants are provided the most favorable conditions for a healthy, rapid growth.
The soil in green houses is fertilized and extremely rich in mineral ions, ensuring healthy, large yields. Extra carbon dioxide is supplied to the crops for faster photosynthesis.
The polythene walls and ceiling permit heat waves and light rays only to enter and stop harmful waves, thereby making available a high light intensity and most favorable temperature, occasionally a heating system is as well utilized.
A watering system is as well made available. The disadvantages of green houses are that it is too small to produce a large yield and that it is costly.
Photosynthetic organisms are known as photoautotrophs, which mean they are capable of manufacturing food directly from carbon dioxide and water using energy from light.
Nevertheless, not all organisms that make of use light as a source of energy carry out photosynthesis, since photoheterotrophs make use of organic compounds, instead of carbon dioxide, as a source of carbon. In plants, algae and cyanobacteria, photosynthesis discharges oxygen.
This process is known as oxygenic photosynthesis. Even though there are a few variations between oxygenic photosynthesis in plants, algae, and cyanobacteria, the overall process is quite similar in these organisms.
However, there are some types of bacteria that carry out anoxygenic photosynthesis, which makes use of carbon dioxide but does not release oxygen.
Carbon dioxide is converted into sugars through a process known as carbon fixation.
Carbon fixation is an endothermic redox reaction, so photosynthesis needs to supply both a source of energy to compel this process, and the electrons required to convert carbon dioxide into carbohydrate.
This addition of the electrons is a reduction reaction. In general outline and in effect, photosynthesis is the opposite of cellular respiration, in which glucose and other compounds are oxidized to manufacture carbon dioxide and water, and to release exothermic chemical energy to propel the organism’s metabolism.
Nevertheless, the two processes occur via a different sequence of chemical reactions and in dissimilar cellular compartments.
The general equation for photosynthesis is therefore:
2n CO2 + 2n DH2 + photons → 2(CH2O) n + 2n DO
Carbon dioxide + electron donor + light energy → carbohydrate + oxidized electron donor
In oxygenic photosynthesis water is the electron donor and, given that its hydrolysis expels oxygen, the general equation for this process is:
2n CO2 + 4n H2O + photons → 2(CH2O)n + 2n O2 + 2n H2O
Carbon dioxide + water + light energy → carbohydrate + oxygen + water
Over and over again 2n water molecules are cancelled on both sides, giving rise to:
2n CO2 + 2n H2O + photons → 2(CH2O)n + 2n O2
Carbon dioxide + water + light energy → carbohydrate + oxygen
Other processes replace other compounds like arsenite for water in the electron-supply role; for instance a few microbes make use of sunlight to oxidize arsenite to arsenate: The equation for this reaction is:
CO2 + (AsO33–) + photons → (AsO43–) + CO
Carbon dioxide + arsenite + light energy → arsenate + carbon monoxide (utilized to build other compounds in subsequent reactions)
Photosynthesis takes place in two stages. In the first stage, light-dependent reactions or light reactions capture the energy of the sunlight and make use of it to manufacture the energy-storage molecules ATP and NADPH.
During the second stage, the light-independent reactions make use of these products to capture and minimize carbon dioxide concentration.

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