Cell Structure and Cell Diversity

What stain is used on a plant cell?

iodine

What stain is used on a animal cell?

Methylene blue

Plant cell example

Onion

Plant cell structure + Organelles

• Cell wall

• Cell membrane

• Cytoplasm

• Nucleus

• Chloroplast

• Ribosome

• Mitochondria

Cell wall

Made of cellulose (polysaccharide). Gives structure and support to cell.

Cell membrane

Made of lipids (phospholipids) and protein. Controls what enters the cell; selectively permeable. (Need to know structure of cell membrane).

Cytoplasm

Liquid medium composed of water (70-95%) in which cell organelles are suspended. Stage 1 (glycolysis) of respiration occurs here.

Nucleus

Brain of cell. Controls activities of cell and contains genetic material in the form of DNA (nuclear DNA) located on structures called chromosomes. Nucleolus is part of nucleus that makes ribosome.

Chloroplast

Contains chlorophyll (gives plants its green colour). Location for photosynthesis. Contains DNA (non-nuclear DNA).

Ribosome

Location for protein synthesis. Does not contain DNA BUT contains RNA.

Mitochondria

Respiration occurs here (2nd stage-Krebs cycle). Contains DNA (non-nuclear DNA).

Animal cell structure + Organelles- e.g. cheek cell

• Cell membrane

• Cytoplasm

• Nucleus

• Mitochondria

• Ribosome

What two organelles are missing from an animal cell compared to a plant cell?

Chloroplasts and cell wall.

Cell Membrane Structure

• Composed of protein and phospholipids

• The selectively permeable gaps in the membrane of a cell or nucleus are called pores.

Eukaryotic Organisms

Organism that has a nucleus and has membrane enclosed cell organelles, e.g. Fungi.

Prokaryotic Organisms

Organism that does not have a nucleus or does not have membrane enclosed cell organelles, e.g. Bacteria.

Parts of the microscope

• Eyepiece/Objective lens

• Stage

• Light/Mirror

• Coarse Focus Wheel

• Fine Focus Wheel

• Diaphragm/condenser

Eyepiece/Objective lens

Magnification of the image to be viewed.

Stage

Holds the slide.

Light/Mirror

Illuminate the content of the slide. The light intensity maybe changed by adjusting the condenser or diaphragm.

Coarse Focus Wheel

To move the stage and roughly focus the image.

Fine Focus Wheel

Improve the clarity of the image.

Diaphragm/condenser

Alters the light intensity reaching the sample on the stage.

Total magnification formula?

= eyepiece x objective lens.

E.g. 500 = 10 × 50

Types of Microscopes

Light + Electron

Light

Found in most school labs. This type of microscope will magnify the object and allow basic detail to be observed such as cell membrane and the nucleus. It will not allow cell organelles such as ribosome and mitochondria to be observed.

Electron

Provides far greater magnification than the light microscope and far more expensive. Will allow cell organelles such as mitochondria and ribosome to be observed.

Expt: Preparation and examination of a plant/animal cell under the microscope.

Apparatus:

Onion, saliva, glass slide X2, dropper, water, iodine, methylene blue, cover slip, microscope.

Method

1. Peel a thin layer (to allow light to pass through) of onion (or rub finger/ swab inside cheek) and place on a glass slide.

2. Add two drops of water (to prevent cells drying out).

3. Place a cover slip over the cells; add to the glass slide slowly at a 45o angle using a mounted needle (cover slip holds cells in place/ protects objective lens of microscope and by adding it at a 45o angle will prevent the formation of air bubbles).

4. Add drops of iodine (plant) or methylene blue (animal) stain using a dropper around the edges of the cover slip. The stain will travel towards the cells naturally (stain helps to highlight cell organelles from cytoplasm especially nucleus).

5. Place glass slide on stage of microscope and turn on light of microscope.

6. Observe under low magnification objective lens using coarse and fine focus wheel to adjust the image.

7. Move to a higher magnification objective lens and improve the clarity of the image using the fine focus (do not use coarse focus wheel at this stage as it will damage the lens).

8. Draw an image of what was observed under microscope.

Results: (Image of cells)

Tissue

Group of similar cells working together to carry out a specific function.

Example in Plants

Vascular tissue (Xylem, phloem), dermal tissue, ground tissue.

Adaptation in Plants

• Xylem has adapted by having walls reinforced with lignin and the vessels lie end-to-end.

• Phloem: contain sieve plates which allow food to pass through.

Example in animals

• Epidermis (part of skin)

• blood

• blood vessels

• bone

• nerves

• muscles

Adaptation in Animal

• Muscles have adapted for cellular respiration by having a large surface area.

• Nervous tissue adapted by having a layer of insulation (myelin sheath) to ensure continuous transmission of electrical messages.

Organ

Group of tissues working together to carry out a function.

Example in Plants

Leaf

Adaptation in Plants

-Large surface area (photosynthesis)

-Waxy cuticle (waterproofs top layer of leaf)

-Stomata (openings in the leaf for gaseous exchange)

Example in animals

• Liver

• Kidney

• Heart

Adaptation in Animal

Heart has thick muscle wall to pump blood around entire body.

System

Group of different organs working together to carry out a specific function.

Example in Plants

Transport system (xylem and phloem).

Adaptation in Plants

-Attraction between water molecules allow water to travel to great heights against the force of gravity

-Roots have a large surface area to facilitate the uptake of a large volume of water

Example in animals

• Digestive system

• Circulatory system

• Respiratory system

• Nervous system

• Excretory system

Adaptation in Animal (Digestive system)

Digestive System

- Large surface area (many villi)

-walls of villi one cell thick (rapid exchange between cells and blood)

-good blood supply (transport)

Tissue culture

Is the growth of cells on a sterile (free from all microorganisms) nutrient medium outside of a living organism-on glassware. Type of cell division involved is mitosis.

In-vitro

Grown on glass ware.

Asepsis

Free from harmful or disease causing microorganisms (Pathogens).

Conditions necessary for tissue culturing

• Suitable nutrients present

• Suitable pH

• Suitable temperature

• Sterile

Uses of tissue culture

• Micropropagation of plants (carrots)

  -Produces large quantities of carrots very rapidly

• Cancer research

• Skin graft

• IVF

Advantages of Tissue culturing

1. Fast

2. Large quantities of cells produced

3. Allows for advancement of medicine or treatment of illness.