Chapter 2- Cell Structure

Question 1

Ultra structure of animal cells

Answer 1

1) plasma (cell surface) membrane
2) rough endoplasmic reticulum
3) smooth endoplasmic reticulum
4) mitochondria
5) Golgi apparatus
6) ribosome
7) lysosome
8) centriole
9) nucleus
10) nucleolus
11) nuclear envelope
12) cytoplasm

Question 2

Ultra structure of plant cells

Answer 2

1) same as animal cells +
2) a cell wall with plasmodesmata (channels to allow exchanging of substances between cells)
3) a vacuole
4) chloroplasts

Question 3

Description + Function of the plasma membrane

Answer 3

Description - mainly made of lipids and proteins. Found on the surface of animal cells

Function- regulates the movement of substances into and out of the cell. It also has receptor molecules on it, which allow it to respond to chemicals like hormones.

Question 4

Description + function of cell wall

Answer 4

Description - a rigid structure that surrounds plant cells. It’s mainly made of cellulose

Function- supports plant cells.

Question 5

Description and function of the nucleus

Answer 5

Description- nucleus is surrounded by the nuclear envelope that has pores. The nucleus contains chromatin. Within the nucleus is the nucleolus.

Function- the nucleus controls the cells activities. DNA contains instructions to make proteins. The pores in the nuclear envelope allow substances eg RNA to move between the nucleus and cytoplasm. The nucleolus makes ribosomes.

Question 6

Description and function of lysosome

Answer 6

Description - a round organelle surrounded by a membrane, with no clear internal structure

Function- contains digestive enzymes. These are kept seperate from the cytoplasm by the surrounding membrane, and can be used to digest invading cells or to break down worn out components of the cell.

Question 7

Description and function of ribosomes

Answer 7

Description - a very small organelle that either free floats in the cytoplasm or is attached to the RER. It’s made up of proteins and RNA. It is not membrane bound.

Function- the site where proteins are made

Question 8

Description and function of the rough endoplasmic reticulum

Answer 8

Description - a system of membranes enclosing a fluid filled space. The surface is covered with ribosomes.

Function- folds and processes proteins that have been made at the ribosomes.

Question 9

Description and function of the Smooth endoplasmic reticulum

Answer 9

Description- similar to RER, but with no ribosomes.

Function- synthesis and processes lipids.

Question 10

Description and function of a vesicle

Answer 10

Description - a small fluid-filled sac in the cytoplasm, surrounded by a membrane

Function- transports substances in and out of the cell and between organelles. Some are formed by the Golgi apparatus or the endoplasmic reticulum, while others are formed at the cell surface.

Question 11

Description + function of Golgi apparatus

Answer 11

Description- a group of fluid-filled, membrane bound flattened sacs. Vesicles are often seen at the edges of the sacs

Functions- it processes and packages new lipids and protein. It also makes lysosomes.

Question 12

Description and function of mitochondria

Answer 12

Description- it is usually oval-shaped. It has a double membrane, the inner one is folded to form structures called cristae. Inside is the matrix, which contains enzymes involved in respiration.

Function- the site of aerobic respiration, where ATP is produced. Mitochondria are found in large numbers in cells that are very active and require a lot of energy.

Question 13

Description and function of chloroplast

Answer 13

Description- a small flattened structure. It’s surrounded by a double membrane, and also has membranes inside called thylakoid membranes. These membranes are stacked up in some parts of the chloroplast to form grana. Grana are linked together by lamellae.

Function- the site where photosynthesis takes place. Some parts of photosynthesis happens in the grana and other parts happen in the Stroma (thick fluid found in chloroplasts)

Question 14

Description and function of centriole

Answer 14

Description- small hollow cylinders, made of microtubules.

Function- involved with the seperation of chromosomes during cell division (produce spindle fibres)

Question 15

Description and function of cilia

Answer 15

Description- small hair like structures found on the surface membrane of some animal cells. They have an outer membrane and a ring of nine pairs of microtubules inside with a pair in the middle

Function- the microtubules allow the cilia to move. This movement is used by the cell to move substances along the cell surface.

Question 16

Description and function of flagellum

Answer 16

Description- they stick out from cell surface and are surrounded by the plasma membrane. Inside they look like cilia. 9+2 structure of microtubules

Function- the microtubules contract to make the flagellum move. Flagella are used like outboard motors to propel cells forward eg when a sperm cell swims

Question 17

How do the organelles work together in protein production

Answer 17

1) proteins are made at the ribosomes. New proteins produced at the RER are folded and processed (eg sugar chains are added) in the RER

2) Then they’re transported from the RER to the Golgi apparatus in vesicles.

3) at the Golgi apparatus, the proteins may undergo further processing (eg sugar chains are trimmed or undergo further processing)

4) the proteins enter more vesicles to transported around the cell to the cell surface membrane.

Question 18

Function of the cytoskeleton

Answer 18

1) the microtubules and microfilamengs support the cell’s organelles keeping them in position

2) they also help to strengthen the cell and maintain its shape

3) they’re responsible for the transport of organelles and materials within the cell. For example the movement of chromosomes when they separate during cell division.

4) the proteins of the cytoskeleton can also cause the cell to move. For example the movement of cilia and flagella is caused by the cytoskeletal protein filaments that run through them.

5) involved in exocytosis and endocytosis

Question 19

Comparison between prokaryotes and eukaryotes

Answer 19

1) prokaryotic cells are small (less than 2 micrometers diameter). Eukaryotic cells are larger (between 10-100 micrometers)

2) prokaryotic cells have DNA that is circular. In eukaryotic cells, DNA is linear

3) prokaryotic cells have no nucleus, eukaryotic cells do have a nucleus

4) prokaryotic cells have a cell wall made up of peptidoglycan. Eukaryotic cells have no cell wall in animals, cellulose cell wall in plants and chitin cell wall in fungi.

5) prokaryotic cells have few organelles and no membrane-bound organelles eg no mitochondria. Eukaryotic cells have may organelles + membrane bound organelles

6) prokaryotic cells have flagella made of the protein flagellin, arranged in a helix. In eukaryotic cells, flagella are made of microtubules arranged in a “9+2” formation.

7) prokaryotic cells have small ribosomes (70s). Eukaryotic cells have larger ribosomes (80s)

Question 20

Features of mitochondria that relate to endosymbiosis theory

Answer 20

1) similar size to bacteria
2) have 70s ribosomes
3) have a double membrane
4) contain their own circular DNA