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The ER system of membranous tubules and sacs

Vacuoles

  1. The most prominent structure in plant cells is the large vacuole.
  2. The vacuole is a large membrane-bound sac that fills up much of most plant cells.
  3. The vacuole serves as a storage area, and may contain stored organic molecules as well as inorganic ions.
  4. The vacuole is also used to store waste. Since plants have no kidney, they convert waste to an insoluble form and then store it in their vacuole – until autumn!
  5. The vacuoles of some plants contain poisons (eg tannins) that discourage animals from eating their tissues.
  6. Whilst the cells of other organisms may also contain vacuoles, they are much smaller and are usually involved in food digestion.


Chloroplasts (and other plastids)

  1. A characteristic feature of plant cells is the presence of plastids that make or store food.
  2. The most common of these (some leaf cells only!) are chloroplasts – the site of photosynthesis.
  3. Each chloroplast encloses a system of flattened, membranous sacs called thylakoids, which contain chlorophyll.
  4. The thylakoids are arranged in stacks called grana.
  5. The space between the grana is filled with cytoplasm-like stroma.
  6. Chloroplasts contain ccc DNA and 70S ribosomes and are semi-autonomous organelles.
  7. Other plastids store reddish-orange pigments that colour petals, fruits, and some leaves.


Multicellular organization

In a unicellular organism, one cell carries out all of the functions of life. In contrast, most cells in a multicellular organism are specialized to perform one or a few functions – more efficiently. Because of cell specialization, the cells of multicellular organisms depend on other cells in the organism for their survival.


Tissue, organs, and organ systems

  1. In most Multicellular Organisms, we find the following organization:
    • Cellular Level: The smallest unit of life capable of carrying out all the functions of living things.
    • Tissue Level: A group of cells that performs a specific function in an organism.
    • Organ Level: Several different types of tissue that function together for a specific purpose.
    • Organ System Level: Several organs working together to perform a function. The different organ systems in a multicellular organism interact to carry out the processes of life
  2. Plants also have tissue and organs, although they are arranged somewhat differently from those of animals – e.g. vascular tissue.
  3. The four plant organs are: Roots Stems Leaves and Flowers


Colonial organizations

  1. A colonial organization is a collection of genetically identical cells that live together in a closely connected group.
  2. Many of the cells of the colony carry out specific functions that benefit the whole colony.
  3. Colonial organisms (e.g. sponges, coral) appear to straddle the border between a collection of unicellular organisms and a true multicellular organism. They lack tissues and organs, but do exhibit the principle of cell specialization.
ORGANELLELOCATIONDESCRIPTIONFUNCTION
Cell wallPlant, not animalOuter layer rigid, strong, stiff made of celluloseSupport (grow tall) protection allows H2O, O2, CO2 to pass into and out of cell
Cell membraneBoth plant/animalPlant – inside cell wall animal – outer layer; cholesterol selectively permeableSupport protection controls movement of materials in/out of cell barrier between cell and its environment maintains homeostasis
NucleusBoth plant/animalLarge, ovalControls cell activities
Nuclear membraneBoth plant/animalSurrounds nucleus selectively permeableControls movement of materials in/out of nucleus
CytoplasmBoth plant/animalClear, thick, jellylike material and organelles found inside cell membraneSupports /protects cell organelles
Endoplasmic reticulum (E.R.)Both plant/animalNetwork of tubes or membranesCarries materials through cell
RibosomeBoth plant/animalSmall bodies free or attached to E.R.Produces proteins
MitochondrionBoth plant/animalBean-shaped with inner membranesBreaks down sugar molecules into energy
VacuolePlant – few/large animal – smallFluid-filled sacsStore food, water, waste (plants need to store large amounts of food)
LysosomePlant – uncommon animal – commonSmall, round, with a membraneBreaks down larger food molecules into smaller molecules digests old cell parts
ChloroplastPlant, not animalGreen, oval usually containing chlorophyll (green pigment)Uses energy from sun to make food for the plant (photosynthesis)

This page has been written by Ian White.