Natural Resources – Biogeochemical Cycles
* The continual cycle of water between the land, the ocean and the atmosphere is called the water cycle.
* The interaction of biotic and a biotic component between the biological and geological world is called Biogeochemical Cycle.
* In the carbon cycle, green plants use carbon dioxide from the atmosphere for photosynthesis and finally release it during respiration.
* The sequence in which nitrogen in the atmosphere is passed into soil and lifeforms, and then released back into the atmosphere, is called the nitrogen cycle.
* The Greenhouse effect keeps the Earth warm to sustain life. The ozone layer blocks the harmful ultraviolet rays from reaching the Earth.
Life Process – Photosynthesis
* The process that helps in carrying out metabolic functions of living organisms is called life processes.
* The process of obtaining energy from food is called nutrition autotrophic nutrition.
* Preparation of organic compounds from inorganic substances is called autotrophic nutrition.
* Heterotrophs depend on autotrophs for nutrition.
* The process of fixation of atmospheric carbon dioxide into carbohydrate in the presence of water, sunlight and Chlorophyll is known Photosynthesis.
* Photosynthesis involves a series of photochemical reactions that consists of two phases: Light and Dark reactions.
* Light reaction takes place in the thylakoids of the chloroplast of the leaves.
* Dark reaction takes place in the stroma of the chloroplast.
* Leaves have small pores called stomata for gaseous exchange.
Light Reaction
* Light reactions are the first stage of photosynthesis. It is the photochemical phase of photosynthesis.
* Light reaction takes place in the thylakoid membranes inside the Chloroplast. It includes photosynthetic pigments that are arranged into two light- harvesting complexes within photosystem I and photosystem II.
* Light reaction consists of the following four stages- Light absorption, water splitting, release of oxygen and formation of high energy intermediates ATP and NADPH.
* Water splitting contributes electrons that replace in PSII and protons that help in ATP and NADPH.
* The process of synthesising high-energy compounds like ATP by cells is called phosphorylation.
* The formation of ATP requires a membrane, a proton pump, a proton gradient and an enzyme, ATPase.
The Calvin Cycle
* Light reaction results in ATP, NADPH and oxygen.
* The ATP and NADPH are utilised in the synthesis of carbohydrate in the presence of carbon dioxide and water.
* The three stages of Calvin Cycle are carboxylation, reduction and regeneration..
* The Calvin Cycle or the dark reaction takes place in the stroma of the chloroplast.
* The formation of a molecule of glucose through Calvin Cycle requires 18 ATP molecules and 12 NADPH molecules.
Factors Affecting Photosynthesis
* Photosynthesis is influenced by several internal and external factors.
Internal factors include:
* Number, size, age and orientation of leaves.
* Mesophyll cells and Chloroplasts
* Internal carbon dioxide concentration
* Amount of Chlorophyll
External factors include:
* Availability of sunlight
* Light intensity
* Incident light
* Temperature
* Atmospheric carbon dioxide concentration
* Water
* Blackman’s Law of limiting Factors state that “If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value. It is the factor which directly affects the process if its quantity is changed.
* At low high intensity, incident light and the rate of photosynthesis are linearly related.
* When C4 plants are subjected to higher temperatures, they register a greater increase in the rate of photosynthesis than C3 plants.
* Water stress caused by lack of sufficient water forces the stomata to close, which automatically means less carbon dioxide for plants.
