cells

• a cell is a unit of life. it consists of a mass of living matter called protoplasm
• Protoplasm:

  • cell membrane
  • cytoplasm 
  • vacuole 
  • nucleus
• Cell membrane:

  • surrounds cytoplasm of cell
  • made up of fats(lipids) and proteins
  • partially permeable membrane
  • allow some substances to pass through
  • controls movement in and out of the cell
• Cell wall:

  • encloses entire plant cell, surrounding the cell membrane
  • made of cellulose
  • protects cell from injury
  • gives plant cell a fixed shape 
  • fully permeable
  • does not control type of substances that enter or leave cell
  • absent in animal cells
• Cytoplasm:

  • jelly like substance, fills inside of cell
  • enclosed by cell membrane 
  • where most cell activities occur
  • contains organelles
• Organelles:

  • cellular structure that performs a specific job within a cell

  Examples:

  • mitochondria 
  • ribosomes
  • vacuole
  • nucleus
• Nucleus:

  • surrounded by nuclear membrane 
  • contains genetic information in the form of chromosomes 

  Functions of nucleus:

  • controls cell activities such as cell growth, repair of worn out parts
  • essential for cell division 
  • cells without a nucleus, like the RBC, are unable to divide
• Nuclear membrane:

  • separates the contents of the nucleus from rest of cytoplasm

  Chromosomes:

  • made up of molecule called DNA(deoxyribonucleic acid) coiled around proteins
  • hereditary information is stored in DNA
  • 46 chromosomes in each human body cell
  • control cell activities
• Vacuole:

  • fluid-filled space 
  • store substances within the cell
  • Plants cells have a large central vacuole which contains cell sap, which contains dissolved substances such as sugars, mineral salts and amino acids 
  • Animal cells have many small vacuoles, contains water and food substances, exist temporarily
• Mitochondria:

  • small oval/ sausage shaped organelles that are bound by a membrane
  • break down glucose in the presence of oxygen -> release energy for cell activities
  • process called aerobic respiration
• Ribosomes:

  • small round structures
  • attached to organelles within cell / lie freely in cytoplasm
  • needed to synthesise proteins in cell
• Chloroplasts:

  • oval structures found in plant cells
  • contain a green pigment -> chlorophyll
  • chlorophyll is essential for photosynthesis -> plants make food
• Differentiation:

  process which by a cell becomes specialised for a specific function
• Root hair cell

  Long and narrow root hair -> increase surface area to volume ratio to absorb water and mineral slats at a higher rate
• Red blood cells:

  • contains haemoglobin which binds oxygen and transports it around the body
  • circular biconcave shape, increases surface area to volume ratio, oxygen can diffuse in and out at a higher rate
  • lacks a nucleus, enable cell to store more haemoglobin for transport of oxygen
  • is flexible, can squeeze through capillaries easily / can change shape to go through blood capillary
• Muscle cell:

  • elongated and cylindrical in shape
  • contains many nuclei and mitochondria
  • has mitochondria to provide the energy for contraction of muscle cell