Summary AS level Cell Structure

Cell Structure
Plant Animal
- Tough cellulose wall present in addition to - Cell wall absent  only cell surface
the cell surface membrane membrane surrounds cell
-Its and plasmodesmata present in the cell - No pits or plasmodesmata as no cell wall
wall
- Large numbers of chloroplasts present - Chloroplasts absent
- Mature cells normally have a large central - Temporary vacuoles, if present, are small
vacuole (single & permanent) filled with cell and scattered throughout the cell
sap which is surrounded by the vacuole
membrane
- Cytoplasm normally confined to a thin - Cytoplasm present throughout the cell
layer at the edge of the cell
- Nucleus at the edge of the cell - Nucleus anywhere in the cell but most
often centrally located
- Centrioles absent (in higher plants) Centrioles present (all animal cells)
- Cilia and flagella absent (in higher plants) - Cilia and flagella may be present
- Starch grains used for carbohydrate - Glycogen granules used for carbohydrate
storage storage
Neither will affect osmotic
potential of the cell


The Nucleus
 May vary in shape, size and position in the cell
 contains the genetic material (DNA) and controls the activities of the cell
 usually spherical in shape and between 10-20 μm in diameter
 Nuclear envelope
 double membrane which surrounds the nucleus
 the outer membrane is continuous with the ER. The ER often has ribosomes
attached to it (rough ER  RER)
 Nuclear pores
 allow passage of large molecules e.g. mRNA Out of the nucleus. The pores are
too small to allow exit of DNA
 typically around 3000 pores in the nuclear membrane  diameter 40-100nm
 Chromatin
 associated with proteins as well as being composed of DNA
 the diffuse form that chromosomes take up when the cell is not dividing
 when the cell divides, the chromatin condenses to form chromosomes
 Nucleolus
 small spherical region within the nucleus (there may be more than one)
 responsible for manufacturing ribosomal RNA and assembling the ribosomes

, Chloroplasts
 Found in eukaryotic cells which can photosynthesise
 flat disks - usually 3-10 μm in diameter and 1m thick
 Chloroplast envelope
 Double membrane
 Controls entry/exit of substances
 Stroma
 Colourless, gelatinous matrix which contains enzymes necessary for the light
independent stage of photosynthesis
 Small, circular piece of DNA, 70S ribosomes and oil droplets are found in the
stroma
 Grana
 Structures that looked like stacks of coins
 typically 50 grana in a chloroplast and each is made up of 100 stacked
flattened sacs called thylakoids or lamellae
 grana carry out the light dependent phase of photosynthesis during which
ATP is produced
 Starch grains act as a temporary store of carbohydrates

Mitochondrion
 Rod-shaped and 1-7m in length and o.5-1m in diameter
 Double membrane
 Controls entry and exit of substances
 Inner membrane is folded to form extensions known as cristae
 Cristae
 Some extend across the whole width of the mitochondrion
 Contain enzymes and other molecules involved in aerobic respiration
 Provide a large surface area for a stage of aerobic respiration known as
oxidative phosphorylation which results in the synthesis of ATP molecules
 Matrix
 Semi-rigid structure containing proteins, lipids, 70S ribosomes and circular
DNA (the 70S ribosomes and circular DNA allows the mitochondria to
synthesize some of its own proteins)
 Many enzymes involved in the Krebs cycle can be found in the matrix
e.g. NAD and co-enzymes




Endoplasmic Reticulum (ER)