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Physiology - Plant Cell Functions

What kind of forces can cause water to move and what units can we use to measure these forces?

  • gravity
  • difference in solute concentration
  • low humidity

     

  • All can be expressed as water potential and measured in terms of pressure which is represented in units of the bar (average pressure of the air at sea level or 70.3 grams per square centimeter) and megapascal (MPa). One megapascal is equal to 10 bars.

What slows down movement of water in living cells?

cellular membranes

What is the relationship between the osmotic properties of cell membranes and plant growth?

Because membranes are semi-permeable, solute concentrations in the cell (especially in the vacuole) cause osmotic uptake of water, leading to cell expansion.

In terms of water potential what happens to a cell during plasmolysis?

The solution outside the cell is at a lower water potential than the cell contents so that water moves out of the cell, down the potential gradient.

When we talk about membranes as a "fluid mosaic", what is flowing and what are the different components of the mosaic?

Membrane proteins float like islands in a sea of lipid.

What kinds of protein move compounds across membranes and how do they do this?

  • ATPases use energy from hydrolysis of ATP to push ions or molecules from one side to the other and are the only way that cells can move them against a concentration gradient.
  • carrier proteins can flip-flop from one side of a membrane to another
  • channel proteins move specific proteins which allow ions or molecules to pass through holes

What other ways might stuff get moved across (plasma) membranes or from cell to cell?

Some molecules can be carried inside membrane vesicles which fuse with a cell membrane and release their contents on the other side.

What are two reasons why we never get the energy out of a system which we put in?

Energy can be converted from one form to another or passed from one molecule to another but some will be released (often as heat)

 

The entropy component deals with the randomness or disorder of a system. Plants expend energy to maintain their highly organized structure at the molecular, cellular and organismal levels.

What is the relation between oxidation and reduction and energy use in living systems?

  • Oxidation involves the loss of an electron, thereby releasing energy. The oxidation of a mole of glucose releases 686 kilocalories of free energy.

     

  • Reduction involves the gain of an electron, thereby storing energy. The reduction of a mole of glucose stores 686 kilocalories of free energy.

     

  • Glycolysis and respiration are oxidation-reduction reactions.

What two properties of enzymes are important for their function in living things?

The enzymes catalyze specific changes in specific molecules (substrates) and they operate at normal temperature.

What kinds of cofactor help enzymes function?

Metal ions and a number of small organic molecules (including NAD).

In what kinds of reaction does NAD participate?

redox reactions

What are two environmental factors which affect the rate of enzyme reactions?

temperature

pH

What is the cell's main energy currency?

ATP

How is the currency "spent" in cellular reactions?

ATP is broken down to ADP and phosphate (often the phosphate is attached to a substrate molecule) to help it in a further reaction.

What are living things mostly made of?

oxygen (mostly as a part of water)

How can cells accumulate nutrients at higher concentration than they occur in their environment?

  1. by passive diffusion
  2. by ATP driven active transport
  3. using carriers or channels

  1. Simple diffusion will tend to equalize concentrations either side of the membrane; energy is required to build up (and maintain) a higher concentration on one side.

     

  2. Yes, any accumulation of a molecule on one side of a membrane is usually driven by a membrane ATPase.

     

  3. Yes, any accumulation of a molecule on one side of a membrane is usually driven by a membrane ATPase.

Cells become differentiated to form specific parts of the plant because they:

  1. contain different genes
  2. make different proteins
  3. divide in different directions

  1. All cells in the plant have the same genetic information, so it is something of a puzzle how they turn out to be different.

     

  2. Yes the proteins are often enzymes that make the cell grow a different shape or produce a different chemical from other cells in the plant

     

  3. Cells do not really begin to differentiate until they have finished dividing.

During mitosis chromosomes line up on a "plate" at the middle of the cell prior to separation of chromatids at:

  1. telophase
  2. prophase
  3. metaphase

  1. Telophase is the end of mitosis when separated chromosomes are reforming nuclei.

     

  2. Prophase is the beginning of mitosis when the nuclear envelope disperses and chromosomes condense.

     

  3. Yes the chromosomes line up at metaphase.

During the 'S' phase of interphase the chromosomes:

  1. are resting
  2. being duplicated
  3. single stranded

  1. They are resting at the beginning of interphase (G1) when there is a single copy and at the end (G2) when there is a double copy of each chromosome.

     

  2. Yes 'S' stands for synthesis when the DNA in the chromosomes is being duplicated.

     

  3. The chromosomes are single stranded at the beginning of interphase (G1).

After mitosis the cell plate that forms between cells is rich in:

  1. pectin
  2. pectin and cellulose
  3. lignin

  1. At first only pectin is formed and this becomes the middle lamella that holds the primary cell walls of adjacent cells together.

     

  2. Cellulose is not formed at first.

     

  3. Lignin is a component of old cell walls.

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