Plant Cell Structure and Photosynthesis

Plant Cell Structure

• Plant cells are eukaryotic cells, possessing a membrane-bound nucleus and other organelles.
• A defining feature is the rigid cell wall composed primarily of cellulose, providing structural support.
• The vacuole, a large central organelle, maintains turgor pressure, contributes to cell growth, and stores nutrients.
• Chloroplasts are unique organelles responsible for photosynthesis, converting light energy into chemical energy.
• Plasmodesmata are cytoplasmic channels connecting adjacent plant cells, facilitating communication and transport.

Photosynthesis

• Photosynthesis is the process converting light energy into chemical energy (glucose).
• Occurs in chloroplasts, specifically the thylakoid membranes where light-dependent reactions occur.
• Plants absorb carbon dioxide from the atmosphere and water from the soil.
• The process involves light-dependent reactions capturing light energy to produce ATP and NADPH, and light-independent reactions (Calvin cycle) using these to convert carbon dioxide into glucose.
• Oxygen is released as a byproduct.

Plant Growth and Development

• Plants exhibit indeterminate growth, continuously growing throughout their lives.
• Meristems are regions of actively dividing cells, responsible for primary (elongation) and secondary (girth) growth.
• Apical meristems are at root and shoot tips, driving lengthening.
• Lateral meristems, like the vascular cambium, increase stem and root width.
• Plant hormones (auxins, gibberellins, cytokinins, abscisic acid) regulate growth and development.

Plant Reproduction

• Plants have diverse reproductive strategies, including asexual and sexual reproduction.
• Asexual reproduction creates genetically identical offspring (runners, tubers, cuttings).
• Sexual reproduction involves gamete fusion (sperm and egg) within flowers, leading to seed formation.
• Flowers are angiosperm reproductive structures, containing male (stamen) and female (pistil) parts.
• Pollination is pollen transfer from anther to stigma, crucial for fertilization.
• Seeds contain the embryo, endosperm (food), and a protective seed coat.

Plant Diversity

• Plants show diverse structures, functions, and reproductive strategies.
• Major groups include non-vascular plants (mosses), vascular plants (ferns), and seed plants.
• Seed plants are divided into gymnosperms (conifers) and angiosperms (flowering plants).
• Adaptations to various environments (water, light, nutrients, temperature) drive plant diversity.
• Plants are essential producers supporting ecosystems and oxygen production.

Plant Adaptations

• Plants have evolved diverse adaptations for survival.
• Xerophytes (arid environments) have thick cuticles, smaller leaves, and water storage tissues.
• Hydrophytes (aquatic environments) have large air spaces for buoyancy and oxygen diffusion.
• Plants in shade have larger leaves for maximum light absorption.
• Carnivorous plants trap insects for nutrients in nutrient-poor soils.
• Plant defenses against herbivores include thorns, spines, chemicals, and toxins.