1.2 ULTRASTRUCTURE OF CELLS

Question 1

Prokaryotic cells

Answer 1

The first organisms to evolve on Earth and have a simple cell structure

DO NOT have a nucleus
Small in size and are found almost everywhere
Ex. soil, water, skin, intestines, pools, volcanic areas

Question 2

Archaebacteria (prokaryote)

Answer 2

Found in extreme environments like high temperatures, salt concentrations or pH

Question 3

Eubacteria (prokaryote)

Answer 3

Traditional bacteria including most known pathogenic forms

Question 4

Cytoplasm

Answer 4

Internal fluid component of the cell

Question 5

Nucleoid

Answer 5

Region of the cytoplasm where the DNA is located (DNA strand is circular and called a genophore)

Question 6

Plasmids

Answer 6

Autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer)

Question 7

Ribosomes

Answer 7

the sites of protein synthesis
(prokaryotic ribosome = 70S) (smaller than eukaryotes)

Question 8

Cell membrane

Answer 8

Semi-permeable and selective barrier surrounding the cell

Question 9

Cell wall

Answer 9

Extracellular structure that encloses the cell, protecting it and
helping to maintain its shape. Prevents the cell from bursting
in hypotonic media

Question 10

Pili

Answer 10

Hair-like extensions that enable adherence to surfaces (attachment pili)

Question 11

Flagella

Answer 11

whip-like structure that is responsible for locomotion

Question 12

Binary fission

Answer 12

a form of asexual reproduction used by prokaryotic cells

Question 13

Steps of Binary Fission

Answer 13

1. The single circular chromosome is replicated
2. The two copies of the chromosome move to opposite ends of the cell
3. Division of the cytoplasm of the cell - The membrane pinches off (cytokinesis), forming two cells
4. Each of the daughter cells contains one copy of the chromosome so they are genetically identical

Question 14

Eukaryotic cells structure

Answer 14

A more complex structure and are believed to have evolved from prokaryotic cells via endosymbiosis

Eukaryotic cells are compartmentalised by membrane-bound structures (organelles) that perform specific roles

Question 15

Nucleus (eukaryotic)

Answer 15

double membrane and has pores

contains chromosomes

it is where DNA is replicated and transcribed to form mRNA

this is exported via the nuclear pores to the cytoplasm

Question 16

Rough endoplasmic reticulum

Answer 16

consists of flattened membrane sacs called cisternae

Attached to the outside of the cisternae, ribosomes (80s)

Main function: synthesise protein for secretion from the cell

synthesised protein is carried in vesicle to the golgi apparatus

Question 17

Golgi apparatus

Answer 17

consist of flattenend membrane sacs called cisternae, however they are shorter and curved and dont have ribosomes attached and have many vesicles nearby

Main function: processes proteins brought form rER

the proteins are carried to the plasma membrane for secretion

Question 18

Lysosomes

Answer 18

spherical with a single membrane

formed from golgi vesicles

they contain high concentrations of protein

They contain digestive enzymes used to break down ingesting food in vesicles

Question 19

Mitochondrion

Answer 19

double membrane

inner contains cristae

the fluid inside is matrix

Main function: produce ATP for the cell by aerobic cell respiration
Fat is digested here if it will be used as energy

Question 20

Microtubules and centrioles

Answer 20

located in cytoplasm

Microtubles main function: moving chromosomes during cell division

Animals contain centrioles: this consits of two groups of 9 triple microtubles

Centrioles form an anchor point for microtubles in cell division

Question 21

Cilia and Flagella

Answer 21

whip-like structure

they contain a ring of 9 double microtubles and 2 in the middle

Flagella is larger and only one is present

Cilia is smaller and many are present

cilia and flagella can be used for locomotion

CIlia can create a curretn in the fluid next to the cell

Question 22

Free ribosomes

Answer 22

synthesise protein

constructed in the nucleolus

Question 23

Chloroplast

Answer 23

double membrane

contains flattened sacs of membrane called thylakoids

produce glucose and other organic compound by photosynthesis

Starch may be present inside

Question 24

Vacuoles and Vesicles

Answer 24

consist of a single membrane with fluid inside

Main function: absorb foods from outside and digest them in vacuoles
Expels excess of water

vesicles are very small vacuoles used to transport materials inside the cell

Question 25

Advantages of compermantalised

Answer 25

1. Flexibility of changing the numbers and position of organelles within the cell based on the cell’s requirements
2. Enzymes and substrates for a particular process can be much more concentrated than if they were spread throughout the cytoplasm.
3. Substances that could cause damage to the cell can be kept inside the membrane of an organelle.
4. Conditions such as pH can be maintained at an ideal level for a particular process, which may be different to the levels needed for other processes in a cell.