cell structures

Question 1

prokaryotic cells vs eukaryotic cells

Answer 1

Prokaryotic:

• no nucleus
• circular dna
• no membrane-bound organelles
• reproduce quickly
• small

Eukaryotic:

• has nucleus bound by nuclear envelope
• linear dna
• many membrane-bound organelles
• relatively large
• reproduce slowly

Question 2

cell surface membrane

Answer 2

• forms the barrier across which all substances entering and leaving the cell must pass
• retains cytosol (aqueous component of cytoplasm)

Question 3

nucleus

Answer 3

• inherited genes on dna in nucleus control protein production and hence the activities of the cell
• largest organelle

Question 4

nuclear envelope

Answer 4

• surrounds nucleus
• a double membrane (outer membrane is continuous with endoplasmic reticulum)
• contains pores that allow for movement of molecules between nucleus and cytoplasm

Question 5

nucleolus

Answer 5

• site where ribosomes are synthesised

- tiny, rounded, darkly-stained body

Question 6

endoplasmic reticulum

Answer 6

• consists of network of folded membranes folded into sheets, tubes/sacs that are extensively interconnected
• continuous with the outer membrane of nuclear envelope
• at the margin, vesicles (small, spherical organelles bounded by single membrane) are formed
• vesicles store & transport substances around the cell

rough endoplasmic reticulum (rER)

• site of protein synthesis in cells
• ribosomes attached on the outer surface of rER are the site of synthesis of proteins that are ‘packaged’ in vesicles
• proteins are folded into their 3D conformation in rER

smooth endoplasmic reticulum (sER)

• site of lipid and steroid synthesis (includes reproductive hormones)
• site of storage of calcium ions in muscle fibres
• no ribosomes

Question 7

Golgi apparatus

Answer 7

• site of synthesis of specific biochemicals (e.g. hormones and enzymes)
• activation of proteins by addition of sugars/by the removal of amino acids
• consists of a stack of flattened membranous sacs
• one face is formed by fusion of membranes of vesicles from rER or sER; vesicles are pinched off opposite the face of the stack
• it is c-shaped
• occurs in all cells

Question 8

mitochondrion

Answer 8

• site of aerobic respiration and ATP synthesis
• contains ribosomes
• rod-shaped/cylindrical
• found in all cells
• double membranous with
  1. smooth outer membrane
  2. infolded inner membrane (cristae)
• matrix: interior of the mitochondrion containing aqueous solution of metabolites and enzymes

Question 9

chloroplasts

Answer 9

• site of photosynthesis: light energy is converted to chemical energy
• double membranous
• continuous outer and inner membrane
• 3rd membranous system of thylakoids (flattened stacks arranged into a geranium, plural grana)
• chlorophyll and pigments located in grana

Question 10

cellulose cell wall

Answer 10

• enclose, support and protect cells
• fully permeable
• in plant cells

Question 11

vacuole

Answer 11

• animal: temporary stores of food/water

- plant: stores nutrients, absorbs water and involved in turgidity