Cell structure

1.1.1 Eukaryotes and prokaryotes

Eukaryotic cell

  • Animal, plant, fungi
  • Has a cell membrane, cytoplasm & genetic material enclosed in a nucleus
  • More complex

1.1.2 Animal and plant cells

Animal cell

Nucleus
  • Contains genetic material (DNA)
  • Control cell’s activities
Mitochondria
  • Where aerobic respiration takes place
  • Releasing energy for cells to work
Cytoplasm
  • Gel-like substance
  • Where chemical reaction takes place
  • Contains enzymes to control chemical reaction
Ribosome
  • Where protein synthesis happens
  • Make proteins using amino acids
Cell membrane
  • Hold cells together
  • Controls movement of substances in & out of cell

Plant cell

Cell wall Supports & strengths cell by cellulose
Permanent vacuole
  • Contains air sap (weak solution of sugar & salt)
  • Keep cells rigid to support plant
Chloroplast
  • Contains chlorophyll that absorb light for photosynthesis
  • Where photosynthesis occurs

Prokaryotic cells

  • Bacteria
  • Have cytoplasm & cell membrane surround by cell wall
  • Genetic material is not enclosed in a nucleus
  • Its DNA is found as a loop in the cell & there may be one or more plasmids

Why are prokaryotic cells smaller & simpler?

  • Larger SA : volume ratio
  • Short diffusion distance
  • Allow sufficient transport of molecules into & out of cell to meet needs of organism

Bacteria cell

Slime capsule Protect cell
Plasmid
  • A small ring of DNA
Flagellum
  • Move themselves around

1.1.3 Cell specialisation

  • Specialisation – cell differentiate to become specialized
  • Animal cells
  • Nerve cells

     

     

    Function

    • Transmit electrical impulses around the body

    Adaptation

    • Have lots of dendrites to connect other nerve cells
    • Axon is very long to cover more distance
    • Synapses contain lots of mitochondria to provide energy to make transmitter chemicals
    • Myelin act as an electrical insulator to stop electrical impulse from leaking out
    Muscle cells

    Function

    • Contract and relax to bring about movement

    Adaptation

    • Contain protein fibre to change length of cell (↓fibre ↓length)
    • Contain many mitochondria to provide energy for contraction and respiration
    • Store glycogen which can be broken down in cellular respiration to transfer energy
    Sperm cells

    Function

    • Carry father’s genetic information and fertilise the egg

    Adaptation

    • Have long tails & streamlined to help swim to egg & reduce cells energy requirements to travel to egg
    • Acrosome contain digestive enzymes to break through egg cell membrane
    • Nucleus contains DNA / 1 set of chromosome to be passed on & preserves the chromosome no when the egg is fertilised
    • Nucleus contains 23 chromosomes
    • Mid-section contains mitochondria to provide energy in respiration for tail to work

Plant cells

Root hair cells

Function

  • To absorb water by osmosis & mineral ions by active transport from soil efficiently

Adaptation

  • Have large SA to absorb water & mineral ions
  • Have large permanent vacuole to speed up movement of water by osmosis
  • Contain mitochondria to provide energy to transport mineral ions into cell
Xylem cells

Function

  • Transport water & mineral ions from root to stems & leaves

Adaptation

  • Have strong lignin spirals which allow them to withstand water pressure to transport water in transpiration stream & support plant stem
  • Cell die & form long hallow tube which is strengthened by lignin spirals allow water & mineral ions to move up easily
  • Few cell structures & so they are dead for more space & supported by lignin
Phloem cells

Function

  • Transport dissolved sugar through translocation from leaves to rest of plant for immediate use or storage

Adaptation

  • Cell walls between cells break down to form sieve plates – allow water carrying dissolved food move freely up & down tube to where it’s needed
  • Companion cells keep them alive & contain mitochondria to provide energy to move dissolved food up & down plant

1.1.4 Cell differentiation

Differentiation

  • Process where cells become specialised for a particular function
  • As an organism develops, cells differentiate to form different types of cells
  • Most types of animal cell differentiate at an early stage
  • Many types of plant cells retain the ability to differentiate throughout life
  • In mature animals, cell division is mainly restricted to repair & replacement
  • As a cell differentiates, it acquires different sub-cellular structures to enable it to carry a particular function. It has become a specialised cell

1.1.5 Microscopy

Microscope

  1. Light microscope
  • Use light & lenses to form image of specimen & magnify

     2. Electron microscope

  • Use electron
  • Have high magnification & resolution
  • Used to study cells in much finer detail & enable biologist to see & understand many more sub-cellular structure

Formula of magnification

  • Magnification = Size of Image / Size of Real Object

Units

  • 1m=1000mm
  • 1mm=1000µm

1.1.6 Culturing microorganisms (biology only)

  • Bacteria in culture medium contains carbohydrates, minerals, proteins & vitamins
  • Cell multiples to form colony
  • Need uncontaminated culture to investigate action of disinfectants & antibiotics

Steps

Pre-inoculation

  1. Sterilize Petri dish & agar before use
  • Kill & prevent unwanted microorganism affect result

       2. Pass inoculating loop through flame

  • Sterilize loop

Inoculation

       3. Use loop to spread bacterium onto agar

  • Open lid as little as possible so fewer bacteria from air to enter

Post-inoculation

        4. Secure lid with tape

  • Prevent bacteria from air to enter

        5. Store Petri dish upside down

  • Prevent drops of condensation fall onto agar surface
  • Growth of bacteria

Calculation – cross-sectional area – πr2

 Why some agar area has no bacteria?

  • Bacteria killed
  • Larger are no bacteria – better
  • Maybe harmful to ppl

In school lab – 25°C – prevent growth of pathogens

In industrial conditions – higher temperature – grow faster