Chapter 3: Cell structure

AS-level - AQA

state 2 examples of eukaryotic cells:

animal cells and plant cells

state 1 example of a prokaryotic cell

bacterial cell

state the organelles found in an animal cell

1. cell wall

2. cell membrane

3. Golgi apparatus

4. lysosomes

5. rough and smooth endoplasmic reticulum

6. nucleus

7. mitochondria

8. ribosomes

state 2 organelles found in plant cells and not animal cells

1. cell wall

2. chloroplasts

3. vacuole

state the cell surface membrane function

controls the movement of substances in and out of the organelle

state the function of the nucleus

contains genetic information for the organism

1. makes mRNA and tRNA

2. makes rRNA and ribosomes

state the structure of the nucleus

1. nuclear envelope → controls the movement of substances in and out the nucleus

2. nucleoplasm

3. nuclear pore → allow large substances to exit the nucleus e.g. mRNA

4. nucleolus → makes rRNA and ribosomes

5. chromosomes → protein-bound linear DNA

state the function of the mitochondria

site of aerobic respiration, produces ATP for energy

state the structure of the mitochondria

1. double membrane → controls the movement of substances in and out of the organelle

2. Cristae → extensions of the inner membrane increases surface area for enzymes in respiration

3. matrix → contains proteins, DNA, lipids and ribosomes

state the function of chloroplasts

absorbs light energy for photosynthesis

state the structure of chloroplasts

1. chloroplast envelope → controls the movement of substances in and out of the organelle

2. thylakoid → light dependent stage takes place

3. granum → stacks of thylakoids

4. stroma → light-independent stage takes place (Calvin cycle)

state the function of Golgi apparatus

1. packs lipids and proteins into vesicles

2. stores and transports lipids and proteins

3. synthesises lysosomes

(modifies proteins)

state the function of lysosomes

breaks down toxins

state the function of ribosomes

protein synthesis

state the structure of ribosomes

1. contains a large subunit and a small subunit

2. contains rRNA

state the function of rER

synthesises and transports proteins

state the function of her

synthesises, stores and transports lipids and carbohydrates

state the function of cell wall in plant cells

1. supports cell

2. prevent cell from bursting

3. allows exchange of substance between cells

state the function of cell vacuole in plant cells

maintains osmotic pressure within the cell

tissue definition

a group of cells that work together to perform a specific function

organ definition

a group of tissues that work together to perform a specific function

organ system definition

a group of organs that work together to perform a specific function

features of eukaryotic cells:

• nucleus

• DNA associated with histone proteins

• DNA is linear

• has membrane-bound organelles

• 80s ribosomes

• DNA has exons and introns

features of prokaryotic cells:

• no nucleus

• DNA not associated with proteins

• circular DNA

• no membrane-bound organelles

• 70s ribosomes

• DNA has exons only

parts of a bacterial cell:

circular DNA →contains genetic info

plasmid →contains gneetic info for adverse survivial conditions

cytoplasm →contains enzymes for chemical reactions

ribosomes → protein synthesis

cell mmbrane → controls movement of chemical in and out of cell

cell wall → protects against damage from other cells and osmotic lysis

capsule → allows bacteria to stick together for protectiona nd protects against other cells

pilli → attatchment to cell substances

flagella → locomotion

viruses are…

acellular and non-living

state the features of a virus:

1. reverse transcriptase

2. genetic material

3. lipid envelope

4. attachment proteins

5. capsid

6. matrix

why are the specimens stained when preparing slides?

to increase contrast and make organelles visible

describe the steps for preparing a mounted slide

1. add a drop of water onto a glass slide

2. add a thin section of specimen to slide

3. add a few drops of stain e.g. iodine

4. lower a coverslip on specimen using a mounted needle

describe the features needed for a biological drawing

1. magnification labelled

2. smooth continuous lines

3. labels which don’t cross

state what type of resolution light microscopes have and why?

they have a low resolution due to long light wavelength

features of light microscopes

1. light wavelength

2. live specimens

3. low resolution

4. shows colour

5. can use thicker specimens

6. uses lenses to focus light

features of TEM microscopes

1. electron beam

2. greater resolution

3. can see smaller organelles

4. views only dead specimens

5. doesn’t show colour

6. thinner specimens

7. more complex and time consuming

8. uses magnets to focus beam

give 3 similarities between TEM and SEM microscopes

1. both are expensive

2. both involve complex sample preparation

3. both produce black and white images

4. both view only dead specimens

magnification definition

a measure of how many times bigger the image is to the object

resolution definition

the ability to distinguish between 2 objects that are close together

magnification formula

image size/ actual size

why does the tissue sample need to be homogenised?

to break open cells and release the organelles

why does the solution need to be filtered

to remove large cell debris

why must the tissue be placed in an ice-cold solution

to slow down enzyme activity to prevent digestion of organelles

why must the tissue sample be placed in a buffered solution

to maintain pH to prevent enzymes being denatured

why must the tissue sample be placed in an isotonic solution

to prevent osmosis so osmotic lysis doesn’t occur

state the process of centrifugation for obtaining mitochondria

1. place tissue sample in a blender and filter

2. place in an ice-cold, buffered, isotonic solution

3. centrifuge at a low speed and remove nucleus pellet

4. centrifuge at a higher speed to obtain mitochondria

what are the 5 stages of mitosis

1. interphase

2. prophase

3. metaphase

4. anaphase

5. telophase

describe the structure of a chromosomes after its been replicated

• made up of 2 sister chromatids attached by a centromere

interphase

• DNA replication occurs

prophase

1. chromosomes condense and become visible

2. nuclear envelope breaks down and nucleolus disappears

3. centrioles move to opposite poles of cells

metaphase

1. chromosomes line up at the equator

2. spindle fibres attach to centromeres

anaphase

1. sister chromatids separate and move to opposite poles of cells

2. by spindle fibres contracting

3. centromeres divide

telophase

1. chromatids reach opposite poles of cell and decondense

2. nuclear envelope forms and nucleolus forms

3. spindle fibres break down and disappear

give three reasons why mitosis is important for living organisms?

1. growth

2. replacement of dead/damaged tissue

3. cloning ar

product of mitosis

2 genetically identical diploid daughter cells

give 2 examples how cancer drugs might affect cell cycle:

1. prevent DNA replication

2. prevent spindle fibre formation

what can mutations in mitosis lead to

uncontrolled cell division causing a tumour

describe the process for binary fission:

1. replication of circular DNA

2. replication of plasmids

3. division of cytoplasm

describe the appearance and behaviour of chromosomes during mitosis

1. chromosomes condense

2. appear as 2 sister chromatids attached by a centromere

3. chromosomes line up across the equator

4. attach to spindle fibres by centromeres

5. centromere divides

6. sister chromatids pulled to opposite poles of cell

7. chromosomes unwind

outline the role of organelles in the production, transport and release of proteins