Cell Structure - Plant Cells

Question 1

What is a chloroplast (what are the characteristics) ?

Answer 1

~they’re visible under a light microscope.
-elongated organelle 3-10nm.
-double membrane -> chloroplast envelope.
-replicate independantly -> own circular DNA.
-70s ribosomes.
-photosynthesis ~light absorbed by chlorophyll in light dependant stage -> ATP.
-uses e- to transport in membranes -> fluid-filled sacs called thylakoids stacked to form grana.
-change orientation of cell -> receive max light.
-light dependant stage -> used the energy and reducing power to convert CO(2) into sugars (Calvin cycle) in the stroma.
-sugars (transported as sucrose in the phloem) stored as starch grains in stroma.
-lipid droplets -> reserves for making membranes.
-originated from endosymbiotic photosynthetic blue-green bacteria.

Question 2

What is a cell wall (what are the characteristics) ?

Answer 2

*first wall -> primary walls.
-rigid -> parallel fibres of polysaccharide cellulose through matrix of pectins and hemicelluloses.
-cellulose -> inelastic and have high tensile strength.
*extra walls -> secondary walls.
-run in different directions forming cross-ply structure (stronger)
-lignin -> more rigid (sclerenchyma or zylem) and adds compressional strength.

Question 3

What are the function of cell walls ?

Answer 3

*Mechanical strength and support:
-lignification
-turgid tissues
-prevent bursting of osmosis.
-different orientations of the layers determines shape of cells as they grow.
-system of interconnnected cell walls -> apoplast and is a transport route for water, inorganic ions
-plasmodesmata -> transport pathway -> symplast
-cell walls of root epidermis impregnated with Suberin -> waterproof substance providing a barrier to movement of water, thus control water and mineral ions uptake.
-epidermal cells -> waxy cutin (cuticle) -> reduce water loss

Question 4

What are vacuoles (what are the characteristics) ?

Answer 4

-animal cells -> small vacuole (phagocytic, food and autographic)
-support -> osmosis causes pressure build up (turgidity)
-lysosomal activity -> may contain hydrolases.
-secondary metabolites -> anthocyanins (pigments~red, purple, pink and blue colours of flowers/fruits)
-alkaloids and tannins -> deter herbivores.
-latex -> rubber trees/tatex of opium poppy contains alkaloids.
-food reserves -> sucrose or mineral salts/protein in seeds.
-waste products -> crystals of calcium oxalates.
-growth in size -> osmotic uptake -> increase in volume.