Cells

Question 1

What is cell theory?

Answer 1

Cell Theory was generally developed around 1838 by Schleiden and Schwann & Virchow
All living organisms are composed of cells and cells form a unifying structural basis of organization.

Question 2

What are Eukaryotic cells?

Answer 2

Eukaryotic - Cells containing a nucleus.
– Organelles - Membrane-bound bodies found within eukaryotic cells.
– Multicellular

Question 3

What are Prokaryotic cells?

Answer 3

Prokaryotic - Cells lacking a nucleus. – Colonies of individual cells

Question 4

Cells in Plants.

Answer 4

• Cells of higher plants generally vary in length between 10 and 100 micrometres.
• Increase in surface area of a spherical cell is equal to the square of its increase in diameter, but its increase in volume is equal to the cube of its increase in diameter.
– Smaller cells have relatively large surface to volume ratios enabling faster and more efficient cellular communication.

Question 5

What is a light Microscopes?

Answer 5

Light Microscopes - Increase magnification as light passes through a series of transparent lenses made of glass

Question 6

What is an Electron Microscope?

Answer 6

Electron Microscopes - Use a beam of electrons produced when high-voltage electricity is passed through a wire.
– Transmission Electron Microscopes - Can produce magnification up to 200,000x, but material must be sliced extremely thin.
– Scanning Electron Microscopes - Offer magnification up to 10,000x but surface detail can be observed on thick objects.

Question 7

What function does the cell wall do?

Answer 7

Cell Wall surrounds protoplasm (contains all living cell components).
– Bound by a plasma membrane (cell membrane)
• Cytoplasm consist of all cellular components between the plasma membrane and the nucleus.
– Cytosol - Fluid within cytoplasm containing organelles.

Question 8

What is the Plasma Membrane?

Answer 8

Plasma Membrane (cell membrane)
– Composed of phospholipids arranged in two layers, with proteins interspersed throughout.
• Some proteins extend across the entire width, while others and embedded to the outer surface.


Question 9

What does the cell nucleus do?

Answer 9

• Nucleus is bound by two membranes, which together constitute the nuclear envelope.
– Structurally complex pores occupy up to one- third of the total surface area.
• Contains fluid nucleoplasm packed with short fibers, and contain larger bodies.
– Nucleoli composed primarily of RNA.
– Chromatin Strands - Coil and become chromosomes.

Question 10

What is Endoplasmic Reticulum?

Answer 10

• Endoplasmic Reticulum facilitates cellular communication and materials channeling.
– Enclosed space consisting of a network of flattened sacs and tubes forming channels throughout the cytoplasm.
• Ribosomes may be distributed on outer surface (Rough ER).
– Associated with protein synthesis.
• Smooth ER is devoid of ribosomes and is associated with lipid secretion.


Question 11

What are Ribosomes?

Answer 11

• Ribosomes are composed of two subunits composed of RNA and proteins.
– Ribosomal subunits are assembled within the nucleolus, released, and in association with special RNA molecules, initiate protein synthesis.
• Have no bounding membranes.


Question 12

What do the Golgi Bodies do?

Answer 12

Golgi Bodies are often bound by branching tubules that originate from the ER.
– Involved in the modification of carbohydrates attached to proteins synthesized and packaged in the ER.
• Polysaccharides are assembled within Golgi bodies, and collect in small vesicles.
– Migrate to plasma membrane and secrete contents to the outside.


Question 13

What are Plastids?

Answer 13

• Chloroplasts are the most conspicuous plastids. – Each bound by double membrane.
• Contain stroma - Enzyme-filled matrix. • Contain grana made up of thylakoids.
– Thylakoid membranes contain chlorophyll.
• Chromoplasts and Leucoplasts are additional plastids found in many plants.


Question 14

What is Mitochondria?

Answer 14

Mitochondria release energy produced from cellular respiration.
– Inward membrane forms numerous folds (cristae).
• Increase surface area available to enzymes in the matrix fluid.


Question 15

What are Endosymbiotic organelles?

Answer 15

• She proposed that: prokaryotes were engulfed by an ancient
eukaryote; or alternatively were invaded by one
• By chance, the two organisms together had a selective advantage; eg: they could survive and reproduce in their niche better than competitors.
• In support of this, mitochondria and chloroplasts have a number of bacterial features:
1. They divide by binary fission
2. Have their own DNA packaged in circular chromosomes (like bacteria!)
3. Own ribosomes which are the same size as bacterial ribosomes 4. Similar size to bacteria.
5. Their membranes have same thickness as bacteria

Question 16

What is Endosymbiosis ?

Answer 16

Endosymbiotic theory suggests engulfed prokaryotes provided hosts with advantages associated with specialized metabolic activities.

Question 17

What are peroxisomes?

Answer 17

Peroxisomes are small, spherical bodies with a single membrane, distributed throughout the cytoplasm which contain specialized enzymes.
– During photosynthesis peroxisomes involved in photorespiration.
– Aid in converting fat to carbohydrates in oilseeds- called glyoxisomes there.
– Many other functions eg. detoxifying byproduct of metabolism, hydrogen peroxide to water and oxygen using – catalase enzyme . Also called microbodies

Question 18

What is the Cytoskeleton?

Answer 18

Cytoskeleton is an intricate network of microtubules and actin microfilaments.
– Microtubules control the addition of cellulose to the cell wall.
– separate chromosomes in mitosis
– Microfilaments play a major role in the contraction and movement of cells in multicellular animals.
• Important role in cytoplasmic streaming.

Question 19

What are Vacuoles?

Answer 19

In mature cells, 90% of volume may be taken up by central vacuoles bounded by vacuolar membranes (tonoplasts).
– Filled with cell sap which helps maintain pressure within the cell.
– Also frequently contains water-soluble pigments.