2.1 cell structure

Question 1

describe the function of the nucleus.

Answer 1

• the nucleus is the most prominent feature of a eukaryotic cell.
• it contains the organism’s hereditary material (DNA), and controls the cells activities.

Question 2

describe the components which make up the nucleus, and explain their functions.

Answer 2

nuclear membrane - a double membrane that surrounds the nucleus, controls the passage of substances in and out of it, and contains the reactions taking place within it.

nuclear pores - allow the passage of large molecules, such as messenger RNA out of the nucleus.

chromosomes - consist of protein-bound, linear DNA.

nucleolus - manufactures ribosomal RNA and assembles the ribosomes.

Question 3

describe the function of the mitochondria.

Answer 3

mitochondria are the main sites of aerobic respiration within the cell, and are responsible for the production of the energy-carrier molecule ATP from respiratory substrates such as glucose.

Question 4

describe what ATP is used for.

Answer 4

ATP is the primary carrier of energy in cells and fuels most cellular processes.

Question 5

describe and explain the structure of the mitochondria.

Answer 5

double membrane - surrounds the organelle, and controls the entry and exit of materials to and from the mitochondrion.

cristae - extensions of the inner membrane which provide a large surface area for the attachment of enzymes, and other proteins involved in respiration.

matrix - contains proteins, lipids, ribosomes, and DNA that allows the mitochondria to control the production of some of it’s own proteins.

Question 6

what type of reaction do chloroplasts carry out in plant cells?

Answer 6

photosynthesis.

Question 7

describe and explain the structure of the chloroplasts.

Answer 7

chloroplast envelope - a double membrane that surrounds the organelle, and controls what enters and leaves the chloroplast.

grana - stacks of disc-like structures called thylakoids, which contain chlorophyll.

stroma - a fluid filled matrix which contains a number of structures, such as starch grains.

Question 8

describe the structure and functions of the endoplasmic reticulum.

Answer 8

• the endoplasmic reticulum is made up of two parts - the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER).
• the RER has ribosomes present on the outer surface of the membrane. it provides a large surface area for the synthesis of proteins and glycoproteins, and a pathway for the transport of materials throughout the cell.
• the SER lacks ribosomes on it’s surface. it synthesises, stores and transports lipids and carbohydrates.

Question 9

describe the structure of the golgi apparatus and give three of it’s functions.

Answer 9

• the golgi apparatus consists of a stack of membranes that make up cisternae, with small, hollow, rounded structures called vesicles.

some of the functions of the golgi apparatus include:

• adding carbohydrates to proteins to form glycoproteins.
• sorting and modifying proteins and lipids.
• forming lysosomes.

Question 10

describe and explain the three main stages of the cell cycle.

Answer 10

interphase - DNA is replicated, ready for cells to divide.

mitosis - cell division takes place.

cytokinesis - the cytoplasm divides, and the cell membrane constricts to form two genetically identical diploid body cells.

Question 11

give three reasons why mitosis is an important process.

Answer 11

• contributes to the growth and repair of tissues.
• replacement and cloning of cells.
• asexual reproduction within an organism.

Question 12

give the four main stages of mitosis.

Answer 12

• prophase.
• metaphase.
• anaphase.
• telophase.

Question 13

describe what happens during prophase.

Answer 13

• the chromosomes coil and condense, each one appearing as two chromatids.
• the nucleolus breaks down, and the centrioles begin to separate and start to form the spindle.

Question 14

describe what happens during metaphase.

Answer 14

• each chromatid is an identical copy of the DNA from the parent cell.
• the chromatids are joined by the centromere, and pulled along the spindle apparatus to line up along the equator of the cell.

Question 15

describe what happens during anaphase.

Answer 15

• the centromeres divide, and the spindle fibres pull the individual chromatids apart.
• the chromatids move to opposite poles of the cell, and are now referred to as chromosomes.
• the energy for this process is provided by mitochondria, which gather around the spindle fibres.

Question 16

describe what happens during the telophase stage of mitosis.

Answer 16

• during telophase, the chromosomes reach their respective poles and become longer and thinner, finally disappearing altogether and leaving behind only widespread chromatin.
• the spindle fibres disintegrate, and the nuclear envelope and nucleolus reform.
• finally, the cytoplasm divides in a process known as cytokinesis until two new identical cells are formed, which once more enter interphase.