Plant Physiological Processes & Soil Fertility

This lesson focuses on growing crops, with an emphasis on maintaining soil fertility, specifically addressing plant physiological processes.
Plant Physiology: A sub-discipline of botany concerned with the physical, chemical, and biological functioning of plants.
Physiological: Relating to the branch of biology that deals with the normal functions of living organisms and their parts.

Photosynthesis involves the utilization of solar energy by chlorophyllous cells in the presence of carbon dioxide and water to synthesize carbon compounds.
A green substance (chlorophyll) uses light energy to change carbon dioxide and water into carbohydrates.
A by-product of this process is oxygen.

Word Equation:
$Sunlight$
$Carbon dioxide + Water \rightarrow Glucose + Oxygen$
$Chlorophyll$
$(Sugar/Carbohydrates)$
Balanced Photosynthesis Equation:
$Sunlight$
$6CO2 + 6H2O \rightarrow C6H{12}O6 + 6O2$
$Chlorophyll$

Transpiration is the evaporation of water from leaves.
It mainly occurs through the stomata.
It has a cooling effect on the leaf cells.
There is a continuous flow of water from the soil into the roots, upward through the roots, stem, and into the leaves. This is known as the transpiration stream.
Stomata: Small openings on the underside of leaves where water evaporates.

Respiration is the oxidation of various substances in the living cell with the release of their chemical energy, carbon dioxide, and water.
Atmospheric air enters through the stomata that occur abundantly on the under surface of leaves. The carbon dioxide diffuses out; during the day, it may be used up in photosynthesis.

$Glucose + Oxygen \rightarrow Carbon Dioxide + Water + Energy$

$C6H{12}O6 + 6O2 \rightarrow 6CO2 + 6H2O + Energy$

Translocation is the movement of organic and inorganic substances from one part of the plant to another.
Xylem vessels carry water and mineral salts up to the leaves to be manufactured into food.
Phloem vessels transport the manufactured food to other parts of the plant to be used or stored.
Xylem: one-way flow; transports water and minerals; no end walls between cells; thick walls stiffened with lignin.
Phloem: two-way flow; transports water and food; cells have end walls with perforations.

Absorption is the process whereby the plant roots take up minerals and water from the soil.
Absorption of salts and water takes place through the root hairs.
These have no protective covering and are in close contact with soil particles.
The soil particles are covered with films of water in which mineral salts are dissolved.
The cell sap is of higher concentration, so water moves into the root hairs and into the root and up to the stem by osmosis.
The mineral salts, as well as water, enter the root hair, not by osmosis but due to the chemical reaction of the salt with the protoplasm and partially to diffusion through the cytoplasmic membrane, which is only selectively permeable.
The roots take in oxygen from the soil air.
Energy assists the root hairs in the uptake of mineral salts from the soil solution.

Plants grow from seeds to seedlings, which in turn grow into mature plants.
Germinating seeds grow by lengthening of their radicle and plumule.
Both root and stem aspects are divided into the region of cell division, cell elongation, and cell maturation.
The region of cell division is also known as the Apical meristem.
An increase in height is brought about by the apical meristem, whereas an increase in girth is by cell division in the cambium.
The cambium layers develop into secondary tissues which may form annual rings.

Photoperiodism is the phenomenon whereby the flowering of plants is regulated by the length of daylight or the mechanism by which organisms respond to seasonal changes in day length.
Certain aspects of the development of many plants, especially flowering plants, are affected by day length.

Short Day: Respond by flowering to short day length (e.g., Maize, Sugar Cane, Sweet Potato, Rice, Pigeon Peas, Sorrel, and Chrysanthemums).
Long Day: Respond by flowering to long day length (approximately 10 hours) (e.g., Radish, Beetroot, Spinach, Onions, Petunias, and Lettuce).
Day Neutral/Photo-insensitive: Does not respond to day length by flowering (e.g., Coconut, Tomato, Melongene, Ochro, and Sweet Pepper).

Phototropism is the growth movement of plants in response to the direction of light.
It allows the maximum exposure to light, which is necessary for photosynthesis.
Phototropism is the ability of a plant, or other photosynthesizing organism, to grow directionally in response to a light source.
Plants and other autotrophs need to manufacture their own food; they usually do this through photosynthesis. Through photosynthesis, organisms convert water, carbon dioxide ( $CO_2$ ) and light into sugars, which are used for energy and growth.
Plants are sessile, meaning they cannot move around to acquire what they need, so in order to maximize the amount of light that they receive through the leaves, they use phototropism.
Positive phototropism is the response of a plant toward a light source, while negative phototropism (also called “aphototropism”) causes growth in the opposite direction.
Plant roots usually use negative phototropism although additionally, they use “gravitropism”, which is the response to gravitational pull.
Auxin plays a role in phototropism by moving towards one side of the plant, causing cells on the darker side to grow faster, leading to bending towards light.
Uniform distribution of auxin makes cells grow evenly.