CIE IGCSE Biology: 复习笔记:2.1.1 Cell Structure

CIE IGCSE Biology: 复习笔记:2.1.1 Cell Structure

Animal & Plant Cells

Animals

  • The main features of animals:
    • They are multicellular
    • Their cells contain a nucleus with a distinct membrane
    • Their cells do not have cellulose cell walls
    • Their cells do not contain chloroplasts (so they are unable to carry out photosynthesis)
    • They feed on organic substances made by other living things
    • They often store carbohydrates as glycogen
    • They usually have nervous coordination
    • They are able to move from place to place

A typical animal cell

Plants

  • The main features of plants:
    • They are multicellular
    • Their cells contain a nucleus with a distinct membrane
    • Their cells have cell walls made out of cellulose
    • Their cells contain chloroplasts (so they can carry out photosynthesis)
    • They feed by photosynthesis
    • They store carbohydrates as starch or sucrose
    • They do not have nervous coordination

A typical plant cell

Cell Structures Found in Both Animal and Plant Cells Table

An animal and plant cell as seen under a light microscope

Cell Structures Found Only in Plant Cells Table

Bacteria Cells

  • Bacteria, which have a wide variety of shapes and sizes, all share the following biological characteristics:
    • They are microscopic single-celled organisms
    • Possess a cell wall (made of peptidoglycan, not cellulose), cell membranecytoplasm and ribosomes
    • Lack a nucleus but contain a circular chromosome of DNA that floats in the cytoplasm
    • Plasmids are sometimes present - these are small rings of DNA (also floating in the cytoplasm) that contain extra genes to those found in the chromosomal DNA
    • They lack mitochondria, chloroplasts and other membrane-bound organelles found in animal and plant cells
  •  Some bacteria also have a flagellum (singular) or several flagella (plural). These are long, thin, whip-like tails attached to bacteria that allow them to move
  • Examples of bacteria include:
    • Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk)
    • Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia)

A typical bacterial cell

Identifying Cell Structures & Function

  • Within the cytoplasm, the following organelles are visible in almost all cells except prokaryotes when looking at higher magnification (ie using an electron microscope):
    • Mitochondria (singular: mitochondrion) are organelles found throughout the cytoplasm
    • Ribosomes are tiny structures that can be free within the cytoplasm or attached to a system of membranes within the cell known as Endoplasmic Reticulum
    • Endoplasmic reticulum studded with ribosomes looks rough under the microscope; this gives rise to its name of Rough Endoplasmic Reticulum (often shortened to R.E.R.)
    • Vesicles can also be seen using a higher magnification - these are small circular structures found moving throughout the cytoplasm

Structures in an animal cell visible under a light microscope and an electron microscope

 

Structures in a plant cell visible under a light microscope and an electron microscope

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