Level 2 NCEA Cell Structure

Level 2 NCEA Cell Structure

1. Cells Structure

   • Cell membrane
     • separates cell & environment
     • 2 layers of lipid molecules (phospholipid bilayer)
       • bilayer is fluid -> allows proteins to move
     • controls entry/exit of substances in & out of the cell
     • semi-permeable- allows passage of only certain substances
       • oxygen, carbon dioxide, glucose, freely diffuse
   • cytoplasm
     • jelly_like fluid
       • water, ions in solution, small molecules & proteins
     • where most of chemical reactions occure
     • supports organelles
   • nucleus
     • largest organelle in cell- double membrane
       • membrane connected to ER
     • many large pores- pass of materials in and out
     • contains genetic material
     • controls cell activities and processes
   • Mitochondria
     • oval shape- increases S.A: Vol ratio
       • so more oxygen can diffuse into mitochondria faster
     • found in large numbers in cells that need a lot of E
       • e.g. sperm, muscle, liver
         • cells lining kidney tubules- very active- reabsorb substances by active transport
     • inner membrane forms folds: cristae
       • increases surface area for enzymes to work on
     • aerobic respiration
     • outer membrane controls exit/entry of materials
     • matrix: fluid filled space inside mitochondria
   • Endoplasmic Reticulum
     • network of membranes running through cytoplasm
     • rough endoplasmic reticulum
       • ribosomes attached- protein production
       • common in cells that make and secrete proteins
         • e.g. digestive cells to produce enzymes
     • smooth endoplasmic reticulum
       • production of lipids
       • common in cells that produce steroid/hormones
         • e.g. oestrogen, progesterone, testosterone
     • functions as a transport system
       • carries materials within cell from nucleus -> outside of the cell
   • ribosomes
     • site of protein synthesis
     • made in nucleus
     • attached to ER
       • making proteins for use inside the cell
     • free in cytoplasm
       • proteins for outside the cell
         • secreted or used in cell membrane
     • made of 2 subunits to form the protein-synthesising unit
   • Golgi body
     • consists of stack of membrane sacs- cisternae
     • after being synthesised most molecules pass through golgi body
     • transports and stores lipids from ER
     • modifies chemicals transported to it from ER and secretes
   • vacuoles
     • fluid filled spaces surrounded by a membrane
     • storage
       • toxic substances- later excreted from cells
       • water, sugars, proteins, salts
       • animal cells- food vacuoles
       • organic compounds, amino acids, inorganic ions
       • pigments
         • e.g. for petals
   • Lysosomes
     • small vacuoles containing digestive enzymes
       • membrane prevents enzymes from digesting cells itself
     • releases enzymes
       • digest/destroy worn-out organelles within the cell
       • digest material taken into the cell
       • e.g. break down ovum membrane to allow sperm head entry
   • PLANT CELLS ONLY
     • Cell wall
       • made of many tiny cellulose fibres made of thousands of cellulose molecules
       • fibres at right angles
         • provide strength
       • provides support to the cell
         • allows it to be turgid without bursting
     • Chloroplasts
       • found in photosynthetic cells
         • plant leaves and stems
       • site of photosynthesis
       • contains grana
         • grana=piles of flattened membranes called thylakoids
         • contains chlorophyll
           • chlorophyll converts light E -> ATP
         • have increased surface area for light absorption
           • increases rate of photosynthesis
       • fluid=stroma
         • contains enzymes involved in final stages of photosynthesis
         • have large starch granules
           • form a temporary store for products of photo synthesis
   • cilia and flagella
     • cilia
       • hair like short found in large numbers
       • create currents
         • move chemicals about/over suface of cell
           • e.g. in the trachea
         • move the cell
     • projecting from surface of some animal/plant cells
     • flagella
       • whip-like 'tails'
       • usually singular
       • move the cell
         • e.g. sperm