Plant Cells, Tissues and Structures

• Plants are complex organisms with specialized structures for survival
• Plants are incredibly diverse, can be found in various sizes and environments, and are essential to life on Earth

Plant Cells and Tissues

• Plant cells have rigid cell walls, chloroplasts for photosynthesis, and large vacuoles
• Chloroplasts enable plants to produce food through photosynthesis
• Plant cells are eukaryotic, like animal cells, containing a nucleus and other organelles
• Tissues are groups of similar cells performing specific functions in an organism
• Plant tissues include:
  • Dermal tissue: provides protection and prevents water loss
  • Vascular tissue: transports water and nutrients
  • Ground tissue: performs various functions, including photosynthesis, storage, and support

Plant Structures: Roots, Stems, and Leaves

• Roots anchor the plant, absorb water and nutrients, and sometimes store food
• Root structures include:
  • Root cap: protects the growing tip
  • Root hairs: increase surface area for absorption
• Stems provide support, transport water and nutrients, and sometimes store food
• Stem structures include:
  • Vascular bundles: contain xylem and phloem for transport
  • Nodes: points where leaves are attached
  • Buds: contain undeveloped leaves or flowers
• Leaves are the primary sites of photosynthesis
• Leaf structures include:
  • Epidermis: outer layer for protection
  • Stomata: pores for gas exchange
  • Mesophyll: contains chloroplasts for photosynthesis
  • Veins: contain vascular tissue for transport

Photosynthesis

• Photosynthesis is the process by which plants convert light energy into chemical energy in the form of glucose
• Photosynthesis equation: 6CO2 + 6H2O + light energy -> C6H12O6 + 6O2
• Chlorophyll, a pigment in chloroplasts, absorbs light energy
• Photosynthesis occurs in two stages:
  • Light-dependent reactions: convert light energy into chemical energy (ATP and NADPH)
  • Light-independent reactions (Calvin cycle): use chemical energy to fix carbon dioxide and produce glucose
• Factors affecting photosynthesis include light intensity, carbon dioxide concentration, and temperature

Plant Reproduction

• Plants can reproduce sexually or asexually
• Sexual reproduction involves the fusion of gametes (sperm and egg)
• Asexual reproduction involves the production of new plants from stems, roots, or leaves (no fusion of gametes)
• Flowers are the reproductive structures of angiosperms (flowering plants)
• Flower parts include:
  • Sepals: protect the developing flower
  • Petals: attract pollinators
  • Stamens: male reproductive structures (anther and filament)
  • Pistil (carpel): female reproductive structure (stigma, style, and ovary)
• Pollination is the transfer of pollen from the anther to the stigma
• Fertilization occurs when the sperm fuses with the egg in the ovule
• The ovule develops into a seed, and the ovary develops into a fruit
• Seed dispersal mechanisms include wind, water, animals, and explosive actions
• Germination is the process by which a seed sprouts and begins to grow

Plant Responses to Stimuli

• Plants respond to various stimuli, including light, gravity, touch, and hormones
• Tropisms are plant responses involving growth towards or away from a stimulus
  • Phototropism: growth in response to light
  • Gravitropism: growth in response to gravity
  • Thigmotropism: growth in response to touch
• Plant hormones regulate growth, development, and responses to the environment
  • Auxins: promote cell elongation and apical dominance
  • Gibberellins: promote stem elongation and seed germination
  • Cytokinins: promote cell division and delay senescence
  • Ethylene: promotes fruit ripening and leaf abscission
  • Abscisic acid: promotes dormancy and closes stomata during water stress

Classification of Plants

• Plants are classified into major groups based on their characteristics
• Major plant groups include:
  • Mosses, liverworts, and hornworts (bryophytes): nonvascular plants that reproduce with spores
  • Ferns, horsetails, and club mosses (seedless vascular plants): have vascular tissue but reproduce with spores
  • Gymnosperms: vascular plants that produce seeds in cones (e.g., conifers, cycads, ginkgoes)
  • Angiosperms: vascular plants that produce flowers and seeds enclosed in fruits (e.g., flowering trees, grasses, vegetables)
• Angiosperms are further divided into monocots and dicots based on several characteristics:
  • Monocots have one cotyledon (seed leaf), parallel leaf veins, scattered vascular bundles in the stem, and flower parts in multiples of three
  • Dicots have two cotyledons, branched leaf veins, vascular bundles in a ring in the stem, and flower parts in multiples of four or five

Importance of Plants

• Basis of food chains, providing energy for other organisms through photosynthesis
• Produce oxygen, essential for animal respiration
• Provide habitats for many organisms
• Used for food, medicine, clothing, shelter, and fuel
• Help prevent soil erosion and maintain water cycles
• Play a role in climate regulation by absorbing carbon dioxide