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