23.1 Biology

• MONOCULTURE: raising a single crop in a large field. It can cause the soil to lose nutrients from year to year. It also encourages the spread of diseases and insect pests.
• Plant organ systems


  • Vascular plants have two distinct organ systems: a shoot system, and a root system
  • The shoot system consists stems, leaves, and the reproductive parts of the plant (flowers and fruits)
  • The shoot system generally grows above ground, where it absorbs the light needed for photosynthesis
  • The root system, which supports the plants and absorbs water and minerals, is usually underground
• Principal organs of plants

  • Stems
  • Leaves
  • Reproductive parts (flowers and fruits)
• Plant tissue systems


  • All three organs (roots, stems, leaves) contain dermal tissue, vascular tissue and ground tissue
• Dermal tissue


  • In young plants consists of a single layer of cells called the epidermis
  • Its outer surfaces are covered with a waxy layer called the cuticle which protects against water loss
  • It is the protective outer covering of a plant
  • In some plants, dermal tissue may be many cell layers deep and may be covered with bark
  • In roots, dermal tissue includes root hair cells that absorb water, passing it along to ground and vascular tissue, where it is carried to the rest of the plant
  • In leaf it has irregular shaped cell with thick outer walls that resist tearing
  • It is protective with cuticle that limits the loss of water through evaporation
• Vascular tissue


  • Includes xylem, a water-conducting tissue, and phloem a tissue that carries nutrients
  • Xylem and Phloem consist of long, slender cells that connect almost like sections of pipe
  • Interactions between vascular tissues support the plant body and transport water and nutrients throughout the plant
  • In the leaf, the vascular tissues are connected directly to the vascular tissues of stems, making them part of the plant's fluid transport system
  • Xylem and phloem cells are bundled in leaf veins that run from the stem throughout the leaf
• Ground tissue


  • Produces and stores sugars and contributes to physical support of the plant
  • In leaf the area between the leaf veins is filled with specialized ground tissue cells known as mesophyll where photosynthesis occurs
  • Ground tissues is divided into three types based on the characteristics of the cell wall: parenchyma, collenchyma and sclerenchyma
  • Parenchyma cells have thin cell walls and a central vacuole surrounded by cytoplasm
  • Collenchyma cells have strong, flexible cell walls that help support plant organs
  • Sclerenchyma cells have extremely thick, rigid cell walls that make tissue like the shells around a walnut seed tough and strong
• Meristems


  • Regions of unspecialized cells in which mitosis produces new cells that are ready for differentiation
  • Found in places where plants grow rapidly such as the tips of stems and roots
  • The tip of the root or stem is the apex known as the apical regions
  • When the pattern of gene expression transforms apical meristems into floral meristems, flower development begins
  • Floral meristems produce a plant's reproductive organs and colorful flower
• Types of root systems

  • Taproot: primary root grows long and thick and gives rise to smaller branch roots (e.g. oak and hickory tree)
  • Fibrous root: the primary root is replaced by branched roots that grow from the base of the stem, branching extensively so no single root grows larger than the rest
• Structure and function of roots

  • Dermal, vascular, and ground tissue are all found in roots
  • A mature root has an outside layer called the epidermis, and also contains vascular tissue and a large area of ground tissue
  • Roots require to take energy from part of the plant to absorb water
  • Roots support a plant, anchor it in the ground, store food and absorb water and dissolved nutrients from the soil
• Uptake of plant nutrients and water movement

  • Soil is a complex mixture of sand, silt, clay, air and organic matter
  • Plants absorb from the soil inorganic nutrients such as nitrogen, phosphorus, potassium, magnesium, sulfur and calcium, and other nutrients called trace elements
  • Vascular cylinder is enclosed by a layer of cells known as the endodermis
  • Where these cells meet, their cell wall form a special waterproof zone called Casparian strip
• Stem


  • Produce leaves, branches, and flowers
  • Hold leaves up to the sun
  • Transport substances throughout the plant
  • Vary in size, shape, and method of development
  • Contain all three tissue systems and distinct nodes, where the leaves are attached
• Tissue arrangement patterns in stems

  • In monocots, clusters of xylem and phloem tissue called vascular bundles are scattered through stem ground tissue
  • In gymnosperms and dicots, vascular bundles are arranged in a ring
• Primary growth


  The primary growth of stems is the result of elongation of cells produced in the apical meristem
• Secondary growth


  • As a plant grows larger, the older stems and roots must increase in thickness as well as in length
  • It is the increase in diameter of the plant body
• Organic matter


  Plants absorb inorganic nutrients such as nitrogen, phosphorus, potassium, magnesium, sulfur and calcium, and other nutrients called trace elements from the soil
• Vascular cylinder


  Enclosed by a layer of cells known as the endodermis
• Casparian strip


  A special waterproof zone where the endodermis cells meet
• Stem


  • Produce leaves, branches, and flowers
  • Hold leaves up to the sun
  • Transport substances throughout the plant
  • Vary in size, shape, and method of development
  • Contain all three tissue systems and distinct nodes where the leaves are attached
• Tissue arrangement in monocots follows a pattern of clusters of xylem and phloem tissue called vascular bundles scattered through the stem ground tissue
• In gymnosperms and dicots, vascular bundles are arranged in a ring
• Primary growth


  The result of elongation of cells produced in the apical meristem
• Secondary growth


  The increase in thickness of stems and roots as a plant grows larger
• Leaf structure


  • Optimized to absorb light and carry out photosynthesis
  • Most leaves have a thin, flattened part called a blade attached to the stem by a thin stalk called a petiole
• Mesophyll tissue


  • Highly specialized for photosynthesis
  • Contains palisade cells that absorb light entering the leaf
  • Contains spongy cells with air spaces that allow gases to move freely
• Stomata


  Small openings in the epidermis that allow carbon dioxide, water, and oxygen to diffuse into and out of the leaf
• Guard cells

  Protect the stomata from opening too far and regulate the movement of gases
• Waxy cuticle


  Prevents water from drowning the plant
• Palisade cells


  Where the majority of photosynthesis happens, packed closely together with many chloroplasts
• Spongy cells


  Also do photosynthesis, with more space in between to allow gases to move freely
• Upper and lower epidermis

  Protect the cells underneath and let sunlight in, while preventing water loss
• Air spaces


  Allow gases to move around freely in the leaf
• Vascular plant


  A plant having a specialized system for carrying fluids that includes xylem and phloem
• Vein (vascular bundle)


  Made up of xylem and phloem tubes that transport sugar and water
• Xylem


  Brings water from the roots through to the leaves
• Phloem


  Transports the sugar made from photosynthesis to various parts of the leaf
• Transpiration


  The loss of water through leaves, which may be replaced by water drawn into the leaf through xylem
• Transpirational pull


  The force in water transport provided by water evaporation from leaves during transpiration
• Cohesion and adhesion


  Work together to pull water upward in plant cells
• Capillary action


  The tendency of water to rise in a thin tube