SNC2D Grade 10 Academic Science Biology Plant Tissues

Biology: Chapter 2 Notes

 

Chapter 2.1—Plant Cells, Tissues and Organs

CELL SPECIALIZATION

  • cell specialization is the process by which cells develop from similar cells into cells that have specific functions within a multicellular organism
  • all body cells in an organism are produced by mitosis, which results in daughter cells with identical genetic information, yet all cells aren’t identical, meaning at some point in their development, cells that start out being the same undergo cell differentiation
  • cell differentiation allows cells to become specialized for different functions
  • cells are specialized according to the set of proteins they contain (genes are responsible for producing these proteins)
    • even though all the cells in an organism contains all the same genes, not all genes are turned on in each cell (one set of genes can be turned on in one cell, and a different set of genes can be turned on in another cell)
    • the proteins produced in a cell determines the eventual function of that cell—the cell is said to be specialized for a specific task

 

SPECIALIZED CELL AND TISSUES IN PLANTS

  • plants are always growing and making new specialized cells (except when dormant due to extreme cold or heat)
  • groups of specialized cells form tissues
    • a cluster of similar cells that share the same specialized structure and function
  • groups of tissues work together in organs (root, stem and leaf)
    • a combination of several types of tissue working together to perform a specific function
  • meristematic cells are responsible for the constant growth of a plant
    • an unspecialized plant cell that gives rise to specific specialized cells
    • known as permanent embryos because of its lifelong ability to produce the cells that can become new tissues and organs in their part of the plant
    • meristematic cells are constantly producing more cells that become specialized; these specialized cells combine to form the 3 types of tissues in the body of the plant
  • the plant has 3 types of tissue: dermal tissue, ground tissue, and vascular tissue
    • dermal tissue
      • forms the outermost covering of the plant’s organs
      • a barrier between the plant and the external environment
      • protects the delicate inner tissue from damage and controls the exchange of water and gases between the plant and its environment
      • epidermis cell is an example of one type of cell that makes up dermal tissue
    • ground tissue
      • has several functions
      • example functions: some ground tissue is made of cells that perform photosynthesis, while other ground tissue is made of cells that provide support for plant body
    • vascular tissue
      • transports water, nutrients and sugars throughout plant
      • provides physical support for plant body as well
    • the cells in each tissue are specialized to perform a specific task (photosynthesis, gas exchange etc.)
  • plants are different from multicellular animals, as they can form cells and tissues (like multicellular animal), but can also form new organs periodically
    • in multicellular animals, the cells, tissues and organs are formed as the embryo develops—some cells and tissues can be repaired/replaced, but organs can’t be replaced
    • ex.: as a leaf gets old, they are replaced by newer leaves that are more efficient
  • plants push upward, downward, and outward because of rapidly dividing meristematic cells at the tips of roots and branches
  • a bud is the swelling of the stem that contains meristematic cells for new (not yet developed) tissues in organs such as leaves and flowers
    • a plant’s most active growth occurs near the terminal bud (at top of plant); the lateral buds are dormant but they have the potential to produce new branches, leaves, and flowers
    • the cells in actively growing areas give off a chemical (auxin) which controls the cells below and behind them—for example, the terminal blood produces auxin to inhibit/holds back the development of cells in lateral buds
      • this allows plants to grow upward rather than outward (if terminal bud removed, lateral bloods would begin to grow, allowing plant to not grow taller anymore, but instead become bushier)

 

TISSUES WORKING TOGETHER: PLANT ORGANS

  • different kinds of tissues combine to make up organs
  • the flower has 3 organs which allow it to grow and live (located in body of plant): leaves, stem, root
  • the flower has a reproductive system, which in most plants is the flower

 

PLANT ORGAN: THE LEAF

  • provides large surface area for photosynthesis to take place
  • if photosynthesis produces more glucose than the leaf needs, the excess is converted into starch and stored in the leaf
  • there are many specialized cells in a leaf
  • the upper and middle leaf
    • the upper surface of a leaf is made of a sheet of dermal tissue called the epidermis
      • they secrete a waxy cuticle that helps reduce the amount of water that evaporates from the leaf’s surface
      • provides plant with protection; doesn’t perform photosynthesis (sunlight passes through epidermis cells)
    • mesophyll tissue is located the upper and lower surface of a leaf
      • consists of palisade tissue cells and spongy parenchyma cells
      • palisade cells (in the shape of poles that support walls) are specialized to perform most of the photosynthesis in leaf
        • the pole shape allows the top of cells to meet Sun’s rays head on, then allowing the rays to pass through the length of the cell
        • as the rays of light journey through the cell, they encounter the many chloroplasts, thus allowing photosynthesis takes place
        • these cells are very active, and therefore contain lots of mitochondria as well for cellular respiration to occur
      • located under palisades, are the parenchyma cells
        • loosely packed, forming a network of open space (like a sponge)
        • the spaces contain the gasses needed/produced by photosynthesis (water vapour, oxygen, carbon dioxide)
      • the centre of the leaf contains the xylem and phloem tissue arranged into the vascular bundle
        • vascular bundles form veins that dissect the interior of the leaf at regular intervals
        • at the tips of the veins are vessels meet open spaces in parenchyma tissue, allowing xylem to deliver water vapour (for photosynthesis), and also allowing phloem to pick up sugars that have been produced (in order to deliver to other cells in the plant)
        • small branches of veins ensure that every cell in the leaf is close to a supply of water and nutrients
  • lower leaf
    • made of an epidermis that is critical for gas exchange between leaf and outside environment
    • to allow gasses to move in and out (carbon dioxide in, and oxygen and water vapour out), guard cells are scattered across the lower surface of the leaf
      • they change shape to control the opening and closing of pores in the leaf (the pores are called stoma)
      • the stomata (plural) are connected to the open spaces of the parenchyma cells
      • guard cells and stomata play a significant role in transpiration (the evaporation of water from leaves)
  • in every cell with chloroplasts, photosynthesis occurs
    • light energy (from the sun) combines with carbon dioxide and water to produce glucose
    • glucose is used by both plants and animal cells as a source of energy (animals don’t make glucose—they eat to acquire the needed glucose)
    • chloroplasts can change shape and location in a cell to increase the amount of light they capture
    • inside the chloroplast are little sacs called thylakoids (which contain light trapping chlorophyll molecules; part where photosynthesis occurs); thylakoids are stacked together (when stacked, called granum)
  • photosynthesis: carbon dioxide + water + light energy  glucose + oxygen

 

PLANT ORGAN: THE STEM

  • has 2 main functions: physical support and transportation of water, nutrients, and sugars
  • the stem contains most of plant’s xylem tissue
    • as xylem cells grow, they form long, straw-like tubes (vessels); when the cells die, their thick cell walls remain behind, forming long fibrous pipes for water to flow through
    • xylem vessels are hollow, so they provide a relatively easy passage through the plant
    • the dead xylem cells are fortified with a hard substance (lignin) which makes them strong, thus keeping the plant upright
  • xylem vessels are grouped with phloem vessels in vascular bundles, further strengthening the stem’s ability to support plant
    • phloem tissue is also made of vertically stacked tubes; their walls are porous allowing materials to be exchanged between phloem and neighbouring cells

 

PLANT ORGAN: THE ROOTS

  • anchor plant to the ground and allow it to take up water and minerals from the soil
  • some roots also act as a plant’s storage area
  • root hairs are the main site of water and mineral absorption
  • cortex cells usually don’t contain chlorophyll; they are used to store starch
    • lots of space between cortex cells to allow for minerals and water to flow through to the endodermis
  • the endodermis helps control the transport of minerals between the cortex and vascular tissue
  • the pericycle is the layer of tissue that surrounds the phloem and xylem
  • there are 2 types of roots:
    • some plants (like dandelions) have a taproot—one main root that grows larger and thicker than the rest
      • allows plant to reach far underground for water
      • anchors plant firmly into ground
    • some plants (like grass) have fibrous roots—the roots spread out horizontally near the surface of the soil
      • provides plant with a large surface area over which water can be taken up from just under the surface of the soil
      • helps stabilize the soil and help to prevent erosion and landslides

 

PLANTS UNDER ATTACK

  • plant tissues and organs can be attacked by viruses (just like animal tissues and organs can)
  • more than 400 viruses cause the 1000 plant diseases
  • not all plant diseases are harmful—in tulips, they get their stripes from a virus
    • other viruses are harmful such as the tobacco mosaic virus
  • plant galls are similar to tumours in animals
    • a gall is an abnormal growth of plant tissue created by insects or micro-organisms
    • plants produce galls in response to attacks by organisms such as insects, fungi, bacteria, and viruses
      • the attackers have a purpose; they use the plant’s resources to support themselves or their offspring (ex.: some insects lay their eggs in trees, allowing the larvae to develop in the galls)
    • insects promote the development of galls by injecting chemicals into the tissue of the plant
      • the chemicals interact with the plant’s fluids and alters which genes are turned off/on in the cells
    • a major difference between plant galls and animal tumours, is that galls don’t spread to other tissues (tumours can as they produce cancer)
      • gall growth is usually contained and the effect on the plant is usually not fatal

 

PLANT ORGAN: THE FLOWER

  • an organ that doesn’t take part in the maintenance of the plant itself
  • its only task is plant reproduction
    • not all plants have flowers for reproduction; some plants reproduce in other ways
  • the different parts of the flower are simply specialized leaves
  • one set of leaves is specialized to produce pollen (sperm), while another set of leaves produce the eggs
  • most plants accomplish pollination with assistance from the wind or animals (birds, insects etc.)
    • through the colour/scent of the flower, insects or other animals are attracted to the plant
      • once there, the animals pick up pollen from the male part of flower; when they later visit another flower, they may transfer this pollen to the female part of the second flower (allowing fertilization to occur)
  • after flower is pollinated, seeds are produced
    • seeds are embedded in fruits
    • ethylene (a hormone) stimulates the ripening of fruits

 

Handouts and Slideshows 

PARTS OF THE FLOWER

  • sepal and petals
  • carpel (female): stigma and ovary which contains ovule
  • anther attached to stamen producing pollen (sperm)