Cell Structure

Question 1

Describe the features of the nucleus?

Answer 1

Nuclear envelope: a double envelope that surrounds the nucleus. Containing about 3,000 nuclear pores that enable large molecules (such as mRNA) to enter and leave. Outer membrane continuous with the endoplasmic reticulum.

Nucleoplasm: Granular, jelly-like material that makes up most of the nucleus under the nuclear envelope

Chromosomes: Protein bound, linear DNA contained in the nucleoplasm

Nucleolus: Small, spherical region within the nucleoplasm. Manufactures RNA and ribosomes.

Question 2

What are the functions of the nucleus?

Answer 2

• Acts as control centre for the cell through the production of mRNA and tRNA that lead to protein synthesis.
• Retains and protects the genetic material of the cell in the form of DNA and chromosomes
• Manufactures ribosomal RNA and ribosomes

Question 3

What is the structure of the mitochondria?

Answer 3

• Organelle with a double membrane that control entry and exit of molecules.
• Inner membrane fold to form extensions called cristae. These provide a large surface area for attachment of enzymes and proteins involved in respiration.
• Matrix, a fluid that contains proteins, lipids, ribosomes and DNA required to allow respiration to occur.

Question 4

What are the functions of Mitochondria?

Answer 4

• Site for aerobic stages of respiration. Responsible for the production of ATP from respiratory substrates such as glucose.
• In cells that have a high level of metabolic activity, number and size of mitochondria (and number of cristae inside) is high to provide a plentiful supply of ATP for processes such as active transport

Question 5

What is the structure of chloroplasts?

Answer 5

• Chloroplast envelope: double plasma membrane that surrounds the organelle and controls the entry and exit of large molecules.
• Grana: stacks of up to 100 disc-like structures called thylakoids, which contain chlorophyll, a photosynthetic pigment. Tubular extensions exist between some thylakoids. It is the location of first stage of photosynthesis.
• Fluid-filled matrix called the stroma. Contains starch grains, and is the location of the second stage of photosynthesis

Question 6

What is the function of chloroplasts?

Answer 6

• Provides large surface areas for the attachment of chlorophyll, electron carriers and enzymes via the granal membrane.
• Fluid of stroma contains the enzymes needed for making sugars in the second stage of photosynthesis.
• Contains both DNA and ribosomes so that proteins needed for photosnythesis can be quickly synthesised.

Question 7

What is the structure of the endoplasmic reticulum?

Answer 7

A network of flattened sacs and tubules (cisternae) enclosed by a three-dimensional system of sheet-like membranes that are continuous with the outer nuclear membrane.

Question 8

What is the difference between the SER and the RER?

Answer 8

• Rough endoplasmic reticulum has ribosomes present on the outer surface of the membranes. Smooth endoplasmic reticulum does not posses ribosomes on its surface and more tubular.
• Rough endoplasmic reticulum provides large surface area for synthesis of proteins and glycoproteins, and acts as a pathway for transport of materials (especially proteins) throughout the cell.
• Smooth endoplasmic reticulum is responsible for the synthesis and storage of lipids and carbohydrates.

Question 9

Describe the structure and function of the Golgi apparatus?

Answer 9

• Series of flattened sacs and vesicles (cisternae)
• Modifies proteins that are passed through it by attaching non-protein components, such as carbohydrates to form glycoproteins.
• Produces secretory proteins and lysosomes
• Transports, modifies, and stores lipids.
• Secretes carbohydrates, such as cellulose for cell walls.

Question 10

What is the structure and function of lysosomes?

Answer 10

• Vesicles produces by the Golgi apparatus containing digestive enzymes, such as lysozymes.
• Hydrolyses material ingested by phagocytes during phagocytosis.
• Sectetes enzymes outside of the cell to destroy material around it.
• Performs autolysis (break down of dead cells) and digests worn-out organelles so their material may be reused

Question 11

Name all of the organelles present in an animal cell

Answer 11

• Nucelus
• Rough endoplasmic reticulum
• Smooth endoplasmic reticulum
• Golgi apparatus
• Mitochondria
• Ribosomes
• Lysosomes
• Centrioles

Question 12

Name all of the organelles present in plant cells

Answer 12

• Nucleus
• Rough endoplasmic reticulum
• Smooth endoplasmic reticulum
• Golgi apparatus
• Mitochondria
• Chloroplasts
• Permanent vacuole
• Ribosomes
• Centrioles

Question 13

What is the difference between eukaryotic and prokaryotic cells?

Answer 13

Eukaryotic cells possess DNA contained in a nucleus, and membrane-bound specialised organelles.

Prokaryotic cells possess DNA that is ‘free’ in the cytoplasm, and does not possess organelles.

Question 14

Describe the structure and function of the cell-surface membrane

Answer 14

‘Fluid mosaic’ phospholipid bilayer with extrinsic & intrinsic proteins embedded between phospholipids

• Separates cytoplasm from external environment
• Possesses molecules used for cell recognition
• Control entry and exit of substances from the cell