Plant Structure and Function

Plant Structure and Function

• Plants have specialized structures for different functions
• Shoots and roots are the main body systems
• Roots absorb water and minerals from the soil, anchoring the plant
• Roots have hair cells to increase surface area for absorption
• Stems support the plant and transport water, minerals, and sugars
• Leaves are the primary sites for photosynthesis; they contain chloroplasts for producing food
• Leaves have specialized cells to produce food via photosynthesis
• Flowers help with reproduction; the undeveloped flower is protected within a bud
• Fruits protect the seeds and are formed from flowers
• The xylem transports water and minerals, and the phloem transports sugars throughout the plant
• Photosynthesis in plants converts light energy into chemical energy (sugar or glucose)
• Plants need a transport system for food, water, and minerals
• Water and minerals are absorbed by roots through osmosis
• Food is produced by leaves via photosynthesis
• Xylem carries water and minerals from roots to leaves
• Phloem carries food from leaves to other parts of the plant

The Leaf

• Typically flat, green, and blade-like
• Attached to a stem, sometimes via a petiole (stalk)
• Main organs for photosynthesis and transpiration
• Photosynthesis: Uses sunlight, carbon dioxide, and water to make glucose (a sugar)
• Gas Exchange: Stomata (small openings) control gas exchange and regulate temperature
• Transpiration: Loss of water vapor through stomata; pulls water up through the plant from the roots
• Food storage: Leaves store food in the form of sucrose for later use
• Waxy cuticle: Transparent, prevents water loss. Protects under the upper epidermis
  • Upper epidermis: Single cell layer, transparent for sunlight, protects the leaf
  • Palisade layer: Contains many chloroplasts, where much photosynthesis occurs
  • Spongy mesophyll: Has airspaces to allow gases to diffuse into leaf tissue
  • Stomata: Tiny pores in the lower epidermis; allow exchange of gases (carbon dioxide, oxygen); controlled by guard cells
  • Guard Cells: Control the opening and closing of stomata
  • Vascular Bundle (vein): Transports water and minerals (xylem) and food (phloem)

Internal Structure of the Leaf

Photosynthesis

• Conversion of light energy into chemical energy
• Occurs in chloroplasts within the leaf
• Raw materials (reactants): Water, carbon dioxide, and sunlight
• End products (products): Glucose (sugar) and oxygen
• Water + Carbon Dioxide + Sunlight → Glucose + Oxygen

Need for Transport Systems in Plants

• Plants need to transport food, water, and minerals throughout the plant.
• Transportation includes:
  • Xylem: Transports water and minerals from roots to leaves
  • Phloem: Transports food from leaves to other parts of the plant

Phloem and Xylem

• Xylem: Dead, hollow tubes; Transports water and minerals from roots to shoots; Provides support
• Phloem: Living cells; Transports sugars (the product of photosynthesis) from leaves to other parts of the plant; Bidirectional transport
  • Phloem and xylem are bundled together in vascular bundles within stems and roots.
• Transportation of food and nutrients, such as sucrose and amino acids from leaves to the roots, storage organs, and growing parts of a plant.

The Stem

• Supports leaves, flowers, and fruits, helps position them correctly for photosynthesis.
• The outer layer is the epidermis; acts as protection for stem
• The vascular bundles give support and flexibility to the stem.
• The vascular bundles are located in the outer regions of the stem
• The pith stores water and sugars (food).
• The cortex surrounds the vascular bundles.
• Cambium tissues: responsible for generating new vascular tissues.

The Roots

• Absorbs water and minerals from the soil.
• Provides anchoring to the ground and support for the plant's structure.
• Contains xylem and phloem vessels
• The outer layer is the epidermis
  • Epidermis cell layer for absorption and protection

Comparing Xylem and Phloem in Stem and Root (Dicots)

• Xylem and phloem are arranged differently:
  • Stem: Xylem usually in the center and phloem towards the periphery.
  • Root: Xylem usually in the center and phloem around it.

Root Hair Cells and Osmosis

• Root hairs increase surface area for water absorption.
• Water moves into the root hairs via osmosis.
• Osmosis: from high water concentration to low water concentration. Water moves from the soil into the root hairs

Factors Causing Water to Rise in Plants

• Root pressure: Water moves into the root cells by osmosis pushing water upwards in the xylem.
• Capillary Action: The ability of water to flow in narrow spaces against gravity
• Cohesion: Water molecules stick to each other; water molecules forming hydrogen bonds
• Adhesion: Water molecules stick to other materials like the xylem walls
• Transpiration: Water loss from leaves through stomata; creates a pulling force that draws water up the xylem from the roots. This happens because water is adhesive and cohesive.