Plant Functions: Photosynthesis and Respiration

• Plants perform several essential functions crucial for their survival and the maintenance of ecosystems.
• These functions include photosynthesis, respiration, transpiration, nutrient absorption, transport, reproduction, and response to stimuli.

Photosynthesis

• Photosynthesis is the process by which plants convert light energy into chemical energy in the form of glucose or sugars.
• This process uses sunlight, water, and carbon dioxide.
• Chlorophyll, a pigment in chloroplasts, absorbs light energy.
• The general equation for photosynthesis is 6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2.
• Photosynthesis occurs in the chloroplasts, specifically in the thylakoid membranes where chlorophyll is located, and in the stroma where glucose is synthesized.
• Carbon dioxide enters the leaves through stomata and water is absorbed by the roots and transported to the leaves.
• Oxygen, a byproduct of photosynthesis, is released into the atmosphere through the stomata.

Respiration

• Respiration is the process by which plants convert the sugars produced during photosynthesis into energy that can be used for growth, repair, and other life processes.
• Plants, like all living organisms, require energy to perform cellular functions
• Respiration involves the breakdown of glucose in the presence of oxygen, releasing energy, carbon dioxide, and water.
• The general equation for respiration is C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP).
• Respiration occurs in the mitochondria of plant cells.
• Plants respire both during the day and night.

Transpiration

• Transpiration is the process by which water is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere.
• This process helps in cooling the plant.
• Transpiration also aids in the transport of minerals and nutrients from the soil to various parts of the plant.
• Water is absorbed by the roots and transported through the xylem vessels to the leaves.
• The rate of transpiration is affected by environmental factors such as temperature, humidity, wind speed, and light intensity.

Nutrient Absorption

• Plants absorb essential nutrients from the soil through their roots.
• These nutrients include macronutrients like nitrogen, phosphorus, and potassium, as well as micronutrients like iron, manganese, and zinc.
• Nitrogen is crucial for the synthesis of proteins, nucleic acids, and chlorophyll.
• Phosphorus is essential for energy transfer, root development, and flower and fruit production.
• Potassium is important for enzyme activation, water regulation, and disease resistance.
• Root hairs increase the surface area for nutrient absorption.
• Nutrients are absorbed in the form of ions dissolved in water.

Transport

• Plants have vascular systems to transport water, minerals, and sugars throughout the plant.
• Xylem transports water and minerals from the roots to the stems and leaves.
• Phloem transports sugars produced during photosynthesis from the leaves to other parts of the plant.
• The transport in xylem is mainly unidirectional, from roots to leaves based on transpiration pull.
• Transport in phloem can be bidirectional, depending on the source (where sugars are produced or stored) and the sink (where sugars are needed for growth or storage).
• Translocation is the process of transport of food (sugar) in plants.

Reproduction

• Plants reproduce either sexually or asexually.
• Sexual reproduction involves the fusion of male and female gametes to produce offspring with genetic variation.
• Asexual reproduction involves the production of offspring from a single parent, resulting in genetically identical offspring.
• Flowers are the reproductive structures of angiosperms (flowering plants), containing stamens (male reproductive organs) and pistils (female reproductive organs).
• Pollination is the transfer of pollen from the stamen to the pistil, which can be mediated by wind, water, insects, or other animals.
• Fertilization occurs when the sperm from the pollen grain fuses with the egg cell in the ovule, leading to the formation of a zygote.
• Seeds develop from the ovules after fertilization, and fruits develop from the ovaries surrounding the seeds.
• Asexual reproduction can occur through various mechanisms, such as vegetative propagation (e.g., runners, rhizomes, tubers) and fragmentation.

Response to Stimuli

• Plants can respond to various external stimuli, such as light, gravity, touch, and chemicals.
• Phototropism is the growth of a plant towards or away from light.
• Gravitropism is the growth of a plant in response to gravity.
• Thigmotropism is the growth of a plant in response to touch.
• Plants use hormones, such as auxins, gibberellins, cytokinins, abscisic acid, and ethylene, to regulate growth and development in response to stimuli.
• Auxins promote cell elongation and play a role in phototropism and gravitropism.
• Gibberellins promote stem elongation, seed germination, and flowering.
• Cytokinins promote cell division and delay senescence.
• Abscisic acid promotes dormancy and helps plants cope with stress.
• Ethylene promotes fruit ripening and leaf abscission.
• Nastic movements are plant responses that are independent of the direction of the stimulus (e.g., the opening and closing of flowers).