Download CHAPTER 15

CHAPTER 13
REVIEW QUESTIONS
13.1
The cell theory states that all living matter is composed of cells and cell products and that all
cells arise from pre-existing ones.
13.2
The inside of the cell and the outside of the cell membrane is in contact with a watery solution.
Each phospholipid molecule is composed of a hydrophilic head and a hydrophobic tail. If there
was only a single layer of phospholipids in the cell membrane, there would be constant forces
of repulsion between the water and the phospholipid tails. With a double layer, the hydrophilic
heads only are in contact with the watery medium and the tails are sandwiched in between,
making a fluid by stable arrangement.
13.3
Proteins act as channels for certain sized water-soluble molecules through the membrane, as
recognition sites, as carrier molecules and sites for enzyme attachment.
13.4
The size of the molecule, its fat-solubility, whether or not it can attach to a carrier protein.
13.5
Different types of phospholipids in the membrane affect its fluidity and permeability – the
more fluid the membrane, the larger the gaps possible between the molecules as they move and
thus the larger the water-soluble molecules that can slip through the phospholipids. Different
integral proteins allow specific substances to pass through them. Differences in peripheral
proteins affect recognition sites and carrier molecules, both of which affect the substances
which can pass through the membrane.
13.6
The cell membrane:
 maintains the integrity of the cell by providing a barrier between the cell contents and the
extracellular environment.
 is a selectively permeable membrane, controlling the movement of chemicals in and out of
the cell
 helps in the active transport of materials across it.
 provides a certain degree of mechanical support to the cell.
 helps the cell to maintain its shape.
 acts as a receptor for certain extracellular materials (e.g. hormones) and thus maintains the
specificity of the particular cell type.
13.7
Some recognition sites:
 are involved in cell-to-cell adhesion in the formation of tissues.
 act as antigens in the immune response.
 are important in control systems: e.g. hormone and other chemical recognition which is
significant in the function of the particular cell type.
13.8
Passive transport does not require energy expenditure by the cell, whereas active transport
does.
13.9
A permeable membrane allows most matter to pass in either direction through it, e.g. a wide
mesh sieve. A selectively permeable membrane only allows certain chemicals to pass through
it, e.g. dialysis tubing.
13.10
In dynamic equilibrium the number of a particular chemical molecule passing through the
membrane is the same in both directions.
13.11
Diffusion is the unaided movement of molecules or ions from a region of their high
concentration to regions of their low concentration. In facilitated diffusion, molecules for
which the membrane is normally impermeable are able to pass from a high to low
concentration across the membrane loosely attached to a globular protein carrier molecule.
13.12
In diffusion there is movement of both solvent and solute through the selectively permeable
membrane. In osmosis, the solute particles are unable to move through the membrane, thus
there is a net flow of water from the low solute concentration (high osmotic potential) to the
high solute concentration (low osmotic potential), i.e. from the hypotonic to the hypertonic
solution.
13.13
a.
b.
c.
Osmosis.
As the amount of water in the plant cell increases, the cytoplasm pushes against the cell
wall. The cell wall exerts an equal and opposite pressure when the turgidity reaches a
particular pressure, thus preventing further water uptake and rupturing of the cell
membrane.
Turgor pressure.
13.14
Active transport may involve carrier molecules in the cell membrane, or the formation or
breakdown of membrane-bound ‘packages' e.g. endocytosis – pinocytosis or phagocytosis;
exocytosis – vacuoles.
13.15
a.
b.
13.16
Both involve the formation of membrane-bound ‘packages’ of matter which can not
normally pass through the cell membrane; they are energy-using processes; they are
means of endocytosis.
In phagocytosis small particles of matter are surrounded by the cell membrane, which
then fuses around the matter and pinches off from the main membrane to form a food
vacuole. In pinocytosis the cell membrane invaginates to form a channel. The ends of the
channel pinch off a fluid-filled vacuole which separates from the main cell membrane.
a.
Structure
Cell wall
Centriole
Chloroplast
Endoplasmic reticulum
Golgi body
Lysosome
Microtubules
Mitochondrion
Nucleolus
Nucleus
Ribosome
Vacuole
Function
Mechanical support and protection; provides
turgor pressure; movement water.
Cilia and flagella formation; cell division.
Converts light to chemical energy in
photosynthesis; oxygen released from water.
Transport; smooth - synthesis lipids and
steroids; rough - transport proteins produced
at ribosomes.
Concentration, packaging and storage of
chemicals.
Intracellular digestion.
Transport and support.
Aerobic respiration.
Ribosome production.
Contains genetic code – controls cell
activities.
Sites protein synthesis.
Storage; water balance.
Usually found in
Animals Plants


some
















small

large
13.17
If the enzymes were free in the cytoplasm they would digest cell organelles.
13.18
Rough endoplasmic reticulum has ribosomes attached to the membrane, whereas smooth
endoplasmic reticulum does not. Thus different parts of the endoplasmic reticulum perform
different functions.
13.19
C: cell walls and central vacuoles.
13.20
Unlike eukaryotic cells, prokaryotic cells do not possess membrane bound organelles, e.g.
nucleus, endoplasmic reticulum, mitochondria etc. If a cell wall is present in eukaryotic cells it
is composed of either cellulose (algae and plants) or chitin (fungi); in prokaryotic cells it is
composed of murein. The chromosomes of eukaryotic cells are multiple, linear and composed
of DNA and protein whilst that of prokaryotic cells is singular, circular and composed of DNA
only. Cytoplasmic streaming occurs in eukaryotic cells but not prokaryotic cells. The
ribosomes of prokaryotes are chemically different to those of eukaryotes. Flagellae in
eukaryotes are complex and composed of microtubules enclosed by the cell membrane whilst
those of prokaryotes are simple and extracellular.
13.21.
The surface area : volume ratio determines the efficiency of diffusion in and out of the cell as
well as movement of materials within the cell and control by the nucleus. The larger the cell
the smaller the SA : Vol ratio and thus the less efficient the cell activities.
13.22
a.
b.
c.
d.
Tissue: group of cells with similar structure specialised to perform a specific function.
Organ: more than one tissue organised into a structural and functional unit.
System: different organs working together for one main function.
Tissue system: group of plant tissues for a function, e.g. phloem.
13.23
a.
A non-cellular matrix may bind cells together or there may be physical connections
between cells.
Plasmodesmata between plant cells and gap junctions between animal cells allows direct
communication between cells. The cell membranes of cells also have recognition sites
which allow communication between cells.
b.
13.24
The cell wall limits movement of plant cells and restricts direct cell to cell communication to
the plasmodesmata. Thus locomotion in plants is not possible. The presence of a cell wall thus
determines the strategies employed by the plant to carry out its life functions.