the ultrastructure of plant cells

• what are plant cell walls made of?

  cellulose
• are cellulose cells walls permeable?

  they are freely permeable, so substances can pass into and out of the cell through the cellulose wall.
• how do cell walls give the plant shape?

  the contents of the cell press against the cell wall making it rigid.
• how is the cell wall a defence mechanism?

  protects the contents of the cell against invading pathogens the cell wall is freely permeable to water, nutrients but is semi permeable to pathogens
• what are vacuoles?

  membrane lined sacs in the cytoplasm containing sap
• why do many plant cells contain large vacuoles?

  so that the contents of the cell push against the cell wall and maintain a rigid framework, maintance of turgor.
• what is the MEMBRANE of a vacuole in a plant cell called?

  tonoplast
• what permeability is the tonoplast?

  selectively permeable, only small molecules can pass through.
• describe what vacuoles are like if they appear in animal cells

  they are small and transient (not permeable)
• what type of membrane structure do chloroplasts have?

  double membrane structure, similar to mitochondria
• what is the fluid enclosed in the chloroplast called?

  stroma
• what are the flattened scacs called that are formed by chloroplasts internal network membranes?

  thylakoids. greek thylakos means ’sac’
• what are several thylakoids stacked together called?

  granum, plural grana
• what are grana joined by?

  membranes called lamellae.
• what do grana contain?

  the chlorophyll pigments, which are where light dependent reactions occur during photosynthesis
• why can chloroplasts make their own proteins?

  they contain DNA and ribosomes
• how are chloroplasts adapted to their function of photosynthesis?

  the internal membranes provide the large surface area needed for the enzymes, proteins, and pigment molecules necessary in the production of photosynthesis.