Cells Structure, Physiology, Molecules And Enzymes

Question 1

What is the Golgi apparatus and where is it found?

Answer 1

• The Golgi apparatus is a series of cisternae (flattened curved sacs)
• Vesicles enter and leave the Golgi. Vesicles carrying protein coalesce on the convex edge, the proteins are modified, and then they are carried away by vesicles from the concave face.

They are found in all eukaryotic cells.

Question 2

What are mitochondria and where are they found?

Answer 2

• Mitochondria are the ‘the power house of the cell’ / site of ATP synthesis during aerobic respiration.
• The mitochondria is enclosed in a double membrane, in which the inner membrane is folded into the matrix. This folds are called Cristae.
• Cristae are more numerous and deeply folded in more active cells.

Mitochondria are found in eukaryotic cells.

Question 3

What is the Endoplasmic reticulum and where is it found?

Answer 3

• The ER is connected to the nuclear envelope and facilitates RNA transport.
• The ER can be Rough (RER) which provides scaffolding for ribosomes to make proteins, or Smooth (SER) Which synthesises cholesterol.

The ER is found in all eukaryotic cells.

Question 4

What is the cell membrane and where is it found?

Answer 4

The cell surface membrane is found in animal cells and
is made of a phospholipid bilayer, with intrinsic and extrinsic proteins.

There are cell membranes in eukaryotic cells.

Question 5

What has an affect on diffusion?

Answer 5

Concentration gradient
Size of molecule
Temperature
Membrane surface area

Question 6

How does facilitated diffusion work?

Answer 6

• Facilitated diffusion can occur through carrier or channel proteins.
• Carrier proteins take in a molecule, change shape and release the molecule on the other side of the membrane.
• Channel proteins have a central pore allowing ions to pass through. Some are gated with opening and closing lids.

Question 7

How does active transport work?

Answer 7

Molecules are transported against the diffusion gradient via pumps. This requires ATP, supplied by mitochondria.

Question 8

What is cytosis and why is it important?

Answer 8

-Cytosis is important because it transports smaller molecules as well as large molecules that carrier proteins cannot transport.
-There are two types of cytosis: exocytosis (materials exiting cell) and endocytosis (materials entering cell).
-In exocytosis secretory vesicles move to fuse with membrane, and substances are released as secretory vesicles merged with the membrane.
-In endocytosis the cell surface membrane invaginates (encloses around) material to form vesicles. There are two types: phagocytosis (solids) and pinocytosis (liquids).
vesicles

Question 9

What is osmosis?

Answer 9

Osmosis is the net movement of water through a selectively permeable membrane from a solution of higher water potential to a solution of lower water potential.

Question 10

What is water potential?

Answer 10

Water potential is effectively the measure of a solution’s tendency to take in water. It is measured in kPa, or Kilopascals. Pure water has 0kPa. Water potential indicates free water molecules.

Question 11

What are free water molecules?

Answer 11

In solutions, hydration shells form around solutes, reducing the amount of free water molecules.

Question 12

What is solute potential, pressure potential and water potential?

Answer 12

• Water potential (Psi cell) is the potential for water to move into a cell.
• Solute potential (Psi s) is the reduction in water’s ability to move, and therefore reducing the water potential value
• Pressure potential (Psi p) is the cell pushing molecules back into the cell, increasing the water potential value.

Question 13

What do the terms turgid and lysis mean?

Answer 13

• Turgid or turgidity is a state in an plant cell when water has effectively filled the cell, and the opposing forces of the cell wall and membrane create turgor.
• Lysis is a state in an animal cell where too much water enters the cell and causes it to burst.

Question 14

What do the terms plasmolysis and crennation mean?

Answer 14

• Plasmolysis is a state in plant cells in which the protoplasm pulls away from the cell wall, and occurs because of an excess of water leaving the cell.
• Crennation is a state in animal cells in which the cell shrinks and shrivels up. This is because too much water has left the cell.

Question 15

What do the terms incipient plasmolysis and flaccid mean?

Answer 15

• Incipient plasmolysis is the point at which the cell membrane just begins to pull away from the cell wall.
• Flaccid describes the state of a plant cell whenever it suffers suffers a shortage of water and loses turgidity, and therefore wilting occurs.

Question 16

What is a hypertonic solution?

Answer 16

A hypertonic solution is a solution in which there is more water present, less hydration shells, less solute concentration and therefore a high water potential.

Question 17

What is the isotonic point?

Answer 17

Where there is no osmosis because the water potential of the cells is exactly equal.

Question 18

What is a hypotonic solution?

Answer 18

A solution in which there is more solute present, more hydration shells, more solute concentration and therefore a low water potential.

Question 19

What is the nucleus, and where is it found?

Answer 19

• The nucleus is the storage container of DNA, in the form of chromatin.
• It is found in eukaryotic cells (plants, animal and fungi cells)

Question 20

What is a chloroplast?

Answer 20

The chloroplast is the organelle responsible for photosynthesis. It is found in plant cells. It contains chlorophyll, which is stored in thykaloids. Many thykaloids form a grana.

Question 21

Describe the structure of a chloroplast

Answer 21

There is a double membrane outer layer, with a stroma suspending grana and the intergranal lamellae.

Question 22

What are ribosomes?

Answer 22

Ribosomes are small organelles either moving freely in the cytoplasm or attached to the RER. They are responsible for protein synthesis.

Question 23

What are lysosomes?

Answer 23

• Tiny vesicles.
• They contain hydrolytic enzymes for internal use.
• They fuse with vesicles holding something that needs to be destroyed or digested.
• They have an important role in phagocytes, where they digest engulfed bacteria.

Question 24

What are microtubules?

Answer 24

• Microtubules are hollow cylinders

- They occur within centrioles and form spindle fibres essential to nulcear division.

Question 25

What are plasmodesmata?

Answer 25

Strands of cytoplasm that extend between neighbouring plant cells

Question 26

What is euchromatin?

Answer 26

Less densely packed chromatin

Question 27

What is heterochromatin?

Answer 27

More densely packed chromatin

Question 28

What is chromatin?

Answer 28

When cells are not dividing chromosomes are organised in a form called chromatin

Question 29

What is a nucleolus?

Answer 29

The nucleolus is the organelle in the nucleus responsible for creating rRNA

Question 30

What is the nuclear envelope

Answer 30

A perforated double membrane that makes up the outer layer of the nucleus

Question 31

Describe 4 differences between eukaryotic cells and prokaryotic cells

Answer 31

Eukaryota: membrane bound nucleus, mitochondria, ER, Golgi apparatus
Prokaryota: Nu nuclei, mitochondria, ER or Golgi, plasmids, glycoprotein wall, slime capsule layer

Question 32

Compare eukaryotic cell structure

Answer 32

Fungi: Cell walls made of chitin, are multi-nucleate, have a vacuole and use glycogen as an energy store
Plants: Cell walls made of cellulose, have chloroplasts and a vacuole, and use starch as an energy store
Animals: No cell walls, only a cell membrane, have no vacuole and have glycogen as an energy store

Question 33

How do you calculate magnification?

Answer 33

M=measured size/real size

Question 34

How is a Light, or optical microscope used in cellular structure examination?

Answer 34

Light is reflected onto glass lenses and the image forms on the retina of the eye. The light microscope has very limited magnification and resolution, but can be used on living specimens. It is also cheap compared to the EM.

Question 35

How is an Electron microscope used in cellular structure examination?

Answer 35

EM beams are reflected by EM lenses, and the image forms on a fluorescent screen. The EM microscope has incredible magnification and resolution, and produces a high quality image of cells and their organelles, however it is expensive and requires its own laboratory, is limited to dead specimens and is suspect to artefacts.

Question 36

What is the difference between the TEM and the SEM?

Answer 36

The TEM (transmission electron microscope) involves electrons passing through thin specimens, producing high res images 
The SEM (scanning electron microscope) involves electrons reflecting off of the specimens. It gives 3D images of surface features.