12.5 studying cells

Question 1

Eukaryotic meaining

Answer 1

means ‘true nucleus’. The DNA of eukaryotes is enclosed by a nuclear membrane. Animal cells are eukaryotic i.e. they have a nucleus. These cells have membrane bound organelles.

Question 2

examples of eukaryotic cells

Answer 2

Plants, algae, animal, protozoan, and fungi

Question 3

Strcture and function of nucleus

Answer 3

Structure
-Nuclear envelope/double
membrane and pores
-Chromosomes / Chromatin (DNA associated with histones) —Nucleolus

Function
-Stores genetic information for polypeptide production.
-Site of DNA replication.
-Site of production of mRNA (transcription) and tRNA.
-Site of production of rRNA/ribosomes (Nucleolus)

Question 4

structure and function of Mitochondrion (singular)
Mitochondria (pleural)

Answer 4

Structure
-Double membrane
-Inner membrane highly folded to form cristae (increase surface area)
-Matrix (liquid part) containing mitochondrial DNA, ribosomes, proteins and lipids.

Function
-Site of ATP production by aerobic respiration.
-Cells that need a lot of ATP have lots of mitochondria. E.g. muscle cells (for muscle contraction) and epithelial cells (for active transport of ions)

Question 5

Smooth Endoplasmic Reticulum structure + function

Answer 5

Structure
-Highly folded membranes flattened into sacks called cisternae

Function
-Recombines glycerol and fatty acids to make triglycerides. ———Packages triglycerides into vesicles and transports them to the Golgi

Question 6

Cytoplasmic Ribosome structure and function

Answer 6

Structure
-Made up of 2 subunits that are made of long strands of rRNA AND ribosomal proteins.
-Eukaryotic cell contains 80s cytoplasmic ribosomes.
Function
-Site of protein synthesis from amino acids.

Question 7

Golgi Apparatus/Body structure and function

Answer 7

Structure
-Flattened sacs made of membrane filled with fluid.
-Golgi vesicles pinch off from the main membrane.

Function
-Sorts, modifies, and packages proteins and triglycerides* into vesicles.
-Golgi vesicles may be used to form lysosomes (see later)..
-Cells with extensive Golgi, packages lots of molecules for export, e.g. enzyme secreting gland cells, or antibodies producing plasma cells.

*Always involves protein.

Question 8

Lysosome structure and function

Answer 8

Structure
-Membrane-bound organelle that stores and releases (many) hydrolytic enzymes.

Function
-Contain hydrolytic enzymes - Phagocytes are types of white blood cells that contain many lysosomes, as they hydrolyse invading pathogens.

Question 9

Cell Surface Membrane structure and function

Answer 9

Structure
-Made up of phospholipids, specific transport proteins, and carbohydrates arranged into what is desribed as a fluid mosaic model (covered in later topic).

Function
-Controls the passage of molecules in and out of the cell

Question 10

Centrioles structure and function

Answer 10

Structure
-Microtubules

Function
-Form a network of spindle fibres onto which chromosomes attach.
Pull chromosomes/chromatids apart during mitosis. These are not found in plant cells

Question 11

what are features of chloroplast?

Answer 11

Granum
Thylakoid membrane
Stroma
Starch grains
DNA and 70s ribosomes

Question 12

Granum

Answer 12

Stack of thylakoid membranes

Question 13

Thylakoid membrane

Answer 13

Contains chlorophyll for photosynthesis & ATP synthase enzyme to produce ATP.

Question 14

Stroma

Answer 14

Fluid filled part, some of the photosynthetic reactions occur her

Question 15

Starch grains

Answer 15

The energy storage molecule in plants.

Question 16

DNA and ribosomes

Answer 16

Contain their own DNA and 70s ribosomes for synthesis of enzymes needed for photosynthesis

Question 17

What are the structural features of an animal cell?

Answer 17

Microvilli
Mitochondria
Golgi apparatus
Cell membrane
Centromere
80s Ribosomes
Nucleus
Nucleolus
Nuclear membrane
Nuclear pores
Rough endoplasmic reticulum
cytoplasm
lysosomes
Smooth endoplamic reticul

Question 18

why is the cell wall strong?

Answer 18

many weak hydrogen bonds

Question 19

what are fungi cell walls made from?

Answer 19

made from chitin not cellulose

Question 20

Key differences between plant and animal cells

Answer 20

-Cellulose cell wall whereas No cell wall
-Chloroplasts present (not in roots) whereas No chloroplasts
-Large central vacuole whereas No large central vacuole
-Carbohydrates stored as STARCH whereas Carbohydrates stored as GLYCOGEN
- Has no centrioles whereas Has centrioles

Question 21

prokaryotes

Answer 21

do not have nucleus or other membrane bound organelles.

The DNA of a prokaryotic cell is circular, and it is not associated with histones.

Question 22

prokaryote vs eukaryote

Answer 22

-DNA is circular and not associated with histones (proteins) whereas DNA is linear (a line) and associated with histones (proteins)
-Contains no membrane bound organelles. (no nucleus, Rough Endoplasmic Reticulum, Smooth Endoplasmic Reticulum, Golgi, Lysosomes) WHEREAS Contains membrane bound organelles I.e., mitochondria, Golgi apparatus, Rough Endoplasmic Reticulum, Smooth Endoplasmic Reticulum, Lysosomes
-Has no ‘true’ nucleus, DNA is free in cytoplasm WHEREAS Has a nucleus, DNA contained within nuclear membrane
- Contains smaller ribosomes (70s) WHEREAS Contains larger ribosomes (80s)
-Some have capsule, one or more flagella, one or more plasmids WHEREAS Do not have capsule
- Has ribosomes for ATP synthesis WHEREAS Does not have ribosomes (has mitochondria)
-Has cell wall made of murein or peptidoglycan WHEREAS Plant cells have a cell wall made of cellulose

Question 23

Name 2 structures found within a eukaryotic cell that cannot be identified using an optical microscope

Answer 23

Any 2 from
Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane

Question 23

Name 2 structures found within a eukaryotic cell that cannot be identified using an optical microscope

Answer 23

Any 2 from
Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane

Question 24

There are 2 types of electron microscope:

Answer 24

1. Transmission Electron Microscope (TEM) produces 2 Dimensional (2D images)
2. Scanning Electron Microscope (SEM) produces 3 Dimensional (3D images)

Question 25

Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure. [5] Principles (how it works) Limitations (drawbacks / disadvantages)

Answer 25

Principles:
1. Electrons pass through / enter (very thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
4. Electrons have short wavelength so give high resolution;

Limitations:
5. Cannot look at living material / Must be in a vacuum;
6. Specimen must be (very) thin; 7. Artefacts present;
8. Complex staining method / complex / long preparation time;

Question 26

Give one advantage of
using a TEM rather than a
SEM.

Answer 26

Higher resolution / higher (maximum) magnification / higher detail (of image); OR Allows internal details / structures within (cells) to be seen / cross section to be taken;

Question 27

Give one advantage of
using a SEM rather than a
TEM.

Answer 27

Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;

Question 28

Scientists use optical
microscopes and
transmission electron
microscopes to investigate
cell structure. Explain the
advantages and limitations
of using a TEM to
investigate cell structure.

Answer 28

Advantages:
1. Small objects can be seen;
2. TEM has higher resolution;
3. Wavelength of electrons shorter;

Limitations:
4. Cannot look at living cells;
5. Must be in a vacuum;
6. Must cut section / thin specimen;
7. Preparation may create artefacts (false image);

Question 29

Describe how you could
make a temporary mount
of a piece of plant tissue to
observe the position of
starch grains in the cells
when using an optical
(light) microscope.

Answer 29

1. Add a drop of water to the microscope slide;
2. Get a thin section of plant tissue and float on the drop of water;
3. Stain with KI solution;
4. Lower the cover slip using a mounted needle to avoid air bubbles;

Question 30

A student viewed impressions of stomata using an optical microscope. She then determined the mean diameter of the stomata. Describe how the student could have used an eyepiece graticule to determine the mean diameter of stomata (3)

Answer 30

1. Measure each stomata using an eye piece graticule
2. Calibrate the eyepiece graticule against a stage micrometer
3. Take at least 5 measurements and calculate a mean (more measurements = more accurate & more representative

Question 31

A student viewed impressions of stomata using an optical microscope. She then determined the mean diameter of the stomata. Describe how the student could have used an eyepiece graticule to determine the mean diameter of stomata (3)

Answer 31

1. Measure each stomata using an eye piece graticule
2. Calibrate the eyepiece graticule against a stage micrometer
3. Take at least 5 measurements and calculate a mean (more measurements = more accurate & more representative

Question 32

Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue (3)

Answer 32

1. Break open the cells in a blender/ homogeniser and filter to remove cellular debris;
2. Place in an ice cold, isotonic, buffered solution;
3. Use differential centrifugation; 4. Chloroplasts are in the second pellet;

Question 33

Scientists isolated mitochondria from liver cells. They broke the cells open in an ice-cold, buffered isotonic solution. Explain why the solution was:
a) Isotonic b) Ice cold c) buffered

Answer 33

1. Prevents osmosis so no osmotic lysis of organelles/named organelle (e.g. mitochondria);
2. Reduce/prevent enzyme activity so organelles are not digested;
3. Maintain a constant pH so proteins are not denatured;