SBI3U Unit 1 Plants

• Chlorophyll in the chloroplasts of plant cells absorbs sunlight which is then used to convert carbon dioxide and water into oxygen and glucose through a light-independent reaction.
• Unique organelles in plant cells:

  • Central Vacuole:
  • LARGE central vacuole stores food, enzymes, and other materials
  • Helps maintain turgor pressure
  • *Animal cells have vacuoles but are much smaller
  • Cell Wall:
  • Structure layer made of cellulose which surrounds the cell to support and protect the plant
  • Chloroplasts:
  • Has a highly folded inner membrane containing chlorophyll which increases the surface area to trap light energy required for photosynthesis
  • Photosynthesis takes place in chloroplast:
• • Water + carbon dioxide + sunlight ---> glucose + oxygen
  • 6H2O + 6CO2 + radiant energy ---> C6H12O6 + 6O2
• • Allows carbon dioxide to diffuse into the leaf for photosynthesis, allows oxygen and water vapor to diffuse out
  • Guard Cells:
  • Sausage-shaped cells that regulate the opening and closing of the stoma
  • When it is humid and these cells are swollen with water, the stoma opens, allowing water vapor to evaporate out
  • When it is really hot and dry and these cells are flaccid, the guard cells close the stoma and prevent evaporation
  • Spongy mesophyll:
• Shoot system (above-ground):

  • Organs:
  • Leaf:
  • Captures light for photosynthesis
  • Allows gas exchange
  • Leaf structure:
  • Palisade mesophyll:
  • Layer of cells near the top of the leaf exposed to the most light
  • Made of parenchyma cells that are packed with chloroplasts with the pigment chlorophyll to maximize light absorption
  • Carries out most of the photosynthesis in the leaf
  • Stomata:
  • Tiny pores in the lower epidermis at the bottom of the leaf
• Spongy mesophyll

  • Airy layer of cells closer to the bottom of the leaf
  • Made of irregularly shaped, chlorophyll-containing parenchyma cells that are loosely packed to create larger air spaces
  • Not as many chloroplasts as cells in palisade mesophyll
  • Vascular bundle:
  • Forms the leaf veins
  • Made of xylem, phloem, and supporting fibers
  • Epidermis:
  • One cell thick layer found on the upper and lower surface of the leaf
  • Covers all leaf surfaces
  • Secretes cuticle to prevent water loss and entry of harmful substances
• 
  

  • Cuticle:
  • Waxy, waterproof substance secreted by the epidermis
  • Covers both upper and lower leaf surfaces
  • Helps to reduce water loss from the epidermis
• Coniferous trees (pine, spruce) have small, needle-like leaves with cutin to prevent water from freezing

  • Stem:
  • Main functions:
  • Structural support
  • Sometimes involved in photosynthesis
  • Bear reproductive structures in mature plant
  • Conduction: xylem transports water and minerals to the leaves, phloem transports food to the roots
  • Food storage
  • Protection
  • Propagation
  • Types:
  • Herbaceous stem:
  • Soft and flexible
  • Green due to the presence of chloroplasts for photosynthesis
  • Found in annual plants and some perennial plants
• 
  

  • Woody stem:
  • Hard and rigid
  • May be covered with bark for protection
  • Found in trees, shrubs, many perennial plants
• Tree Rings:

  • Tree grows in diameter when meristematic tissue in vascular cambium divides to produce new xylem and phloem
  • Annual ring represents one year's growth = earlywood (light band) + late wood (dark band)
  • Thinner ring indicates lower precipitation, wider ring indicates sufficient rainfall
  • Growth varies by season:
  • Late spring/summer: faster growth with thin-walled, large diameter cells
  • Later summer/autumn: slower growth with thick-walled, small diameter cells
  • Winter: dormant (no growth)
• • Casparian strip:
  • A hydrophobic strip, continuous barrier made of a wax-like substance that forces all substances to pass through the plasma membrane and cytoplasm of endodermal cells to enter the vascular cylinder
  • Endodermis:
  • Single layer of cells, innermost layer of the cortex
  • All substances must pass through these cells to enter the vascular cylinder
  • Pericycle:
  • Layers of cells that surround the vascular cylinder, provides support, structure, and protection
  • Cortex:
• Root system (underground):

  • Organs:
  • Root:
  • Anchorage
  • Absorption and transport
  • Storage
  • Root cap:
  • Structure that protects the tips of the root as the root grows
  • Meristematic region:
  • Region of cells that are actively dividing to allow the root to grow in length
  • Zones of elongation:
  • Cells growing longer
  • Zones of maturation:
  • Region of cells developing into different types of root tissues that perform different functions
  • Vascular cylinder:
  • Contains plant's conducting tissue
• Cortex

  • Layer of parenchyma cells found beneath the epidermis, stores water/minerals/food, and helps transport water and minerals
  • Epidermis:
  • Outermost layer of the root, protects inner cells and absorbs water and minerals
  • Root hair:
  • Specialized epidermal cells that greatly increase the surface area of the root for faster absorption
• Types of Root Systems:

  • Taproot:
  • Single thick primary root with smaller lateral branches called secondary roots
  • Stores food and water
  • Grows deep underground
  • Anchors plant
  • Fibrous root:
  • Many smaller branching roots that grow from a central point
  • Do not grow as deeply
  • Covers a large surface area near the soil surface
  • Anchors plant
  • Modified Root:
  • Contains Aerenchyma: spongy soft tissue with large air spaces for buoyancy and gas circulation in aquatic plants
  • Many smaller branching roots that grow from a central point
• Modified roots

  • Stores food and water
  • Absorbs water and minerals
  • Varies in appearance, structure, and function
  • May be specialized for different functions such as food and storage
• Plant tissues:

  • Types of plant tissues include dermal, ground, and vascular tissues
  • Dermal tissue: outer layers of cells that protect the plant
  • Ground tissue: multi-functional tissue made of all cell types, including parenchyma, collenchyma, and sclerenchyma cells
  • Vascular tissue: transports water, minerals, and other substances, includes xylem and phloem in vascular bundles
• Ground tissue:

  • Forms most of the plant's internal and external material with all cell types
  • Acts as a "filter" tissue between dermal and vascular tissues
  • Functions include storage, photosynthesis, and support
  • Ground tissue cells in some stems, roots, and seeds store starch and oils
• Types of ground tissue cells:

  • Parenchyma cells:
  • Found in leaves and green stems with many chloroplasts
  • Found in roots and fruits without chloroplasts but with large central vacuoles for storage
  • Majority of cells in plants are parenchyma cells
  • Functions include storage, photosynthesis, gas exchange, and protection
• • Collenchyma cells:
  • Elongated cells that provide support for surrounding cells
  • Flexibility due to unevenly thickened cell walls
  • Aid in tissue repair and replacement
  • Sclerenchyma cells:
  • Thick secondary cell walls with lignin for toughness
  • Provide support for mature plants
  • Types include sclereids (stone cells) and fibres
• Meristematic tissue:

  • Embryonic tissue that allows for the production of new cells by mitosis
  • Found in meristems, areas of rapidly dividing cells
  • Primary growth increases stem and root length, while secondary growth increases diameter
  • Apical, intercalary, and lateral meristems contribute to plant growth
• Dermal tissue:

  • Outer layers of cells that form a protective covering
  • Includes epidermis and periderm
  • Functions to prevent water loss
  • Specialized epidermal tissues include guard cells, trichomes, and root hairs
• Vascular tissue:

  • Internal system of tubes that transport water and dissolved substances throughout the plant
  • Xylem is water-conducting tissue, while phloem is food-conducting tissue
  • Xylem consists of vessel elements and tracheids, while phloem consists of sieve tube elements and companion cells
  • Xylem transports water and minerals from roots to leaves, while phloem transports sugars made by photosynthesis
• Monocots vs. Dicots:

  • Monocots have one cotyledon in the embryonic seed, parallel leaf venation, fibrous root system, and flower parts in multiples of three
  • Dicots have two cotyledons, netlike leaf venation, taproot system, and flower parts in multiples of four or five
  • Vascular bundle organization differs in stems and roots between monocots and dicots
• Xylem vascular bundles in roots are found in the center, tough, and help prevent the plant from being pulled out of the ground
• In stems, xylem vessels are nearer to the edge, providing strength and support to resist being squashed and bent
• Different scales of transport in plants include:

  • Cellular level: transport of water and solutes into root hairs
  • Short-distance transport: loading of sugar from photosynthesis leaves into phloem sieve tubes
  • Long-distance transport: transport in xylem and phloem throughout the whole plant
• Passive transport in plants, like diffusion, involves solute molecules moving from high to low concentration down its concentration gradient
• Osmosis in plants involves solvent molecules (water) moving from low to high solute concentration, affecting cell turgidity and shape
• Transport in the xylem involves water entering roots via osmosis, then being transported to the stem and leaves for photosynthesis
• Active transport in plants requires energy to move materials across cell membranes against their concentration gradient
• Root pressure, a positive pressure, aids in pushing water and minerals upwards through xylem against gravity, assisted by adhesion
• Transpiration pull, a negative pressure, allows for long-distance water transport in plants, influenced by environmental and physical factors
• The cohesion-tension model explains how transpiration pull and cohesion between water molecules in xylem tubes aid in water transport in plants
• Phloem transportation involves translocation of sucrose and organic molecules from source to sink, regulated by the pressure-flow model