2- eukaryotic cell structure and functions

Question 1

ultrastructure of eukaryotic cells

Answer 1

• cell membrane
• cytoplasm
• nucleus
• chromatin
• nucleolus
• 80s ribosomes
• rough endoplasmic reticulum
• smooth endoplasmic reticulum
• mitochondria
• centrioles
• microtubules
• lysosomes
• golgi apparatus
• vesicles

Question 2

cell membrane

Answer 2

• a selectively permeable layer on the surface around the cell
• formed from a phospholipid bilayer
• forms an outer boundary between the cytoplasm and the outside
• selectively controls and regulates the movement of substances
• flexibility allows the cell to change shape, such as during phagocytosis

Question 3

cytoplasm

Answer 3

• a living, jelly-like material that contains enzymes, water and solutes
• supports organelles and is when chemical reactions take place
• cytoplasm and nucleus are together known as the protoplasm

Question 4

nucleus

Answer 4

• stores DNA, and controls cellular activity by determining the proteins produced
• surrounded by a double membrane called the nuclear envelope, which contains pores
• contains chromatin and a nucleolus

Question 5

chromatin

Answer 5

• DNA packaged with histones
• DNA + histones -> nucleosomes -> chromatin -> chromosomes

Question 6

nucleolus

Answer 6

• an extra dense area of almost pure DNA and protein
• appears as a darkly stained region when observed under microscopes
• site of rRNA and ribosome production

Question 7

80s ribosomes

Answer 7

• composed of a large 60s subunit and a small 40s subunit
• the site of protein synthesis

Question 8

rough endoplasmic reticulum

Answer 8

• a series of flattened sacs enclosed by a membrane with ribosomes on the surface
• folds and processes proteins made on the ribosomes

Question 9

smooth endoplasmic reticulum

Answer 9

• a series of flattened sacs enclosed by a membrane
• synthesises and processes lipids and steroid

Question 10

mitochondria

Answer 10

• site of aerobic respiration
• found in large numbers in active cells

Question 11

centrioles

Answer 11

• there is a pair near the nucleus
• one centriole is a hollow cylinder made up of a ring of nine microtubule triplets
• two arranged at right angles to each other to form a centrosome
• during cell division, they pull apart to produce a spindle of microtubules

Question 12

microtubules

Answer 12

• form the cytoskeleton
• determine and maintain the shape of the cell
• provide routes along which granules and vesicles can be transported
• tubulin (protein) -> dimers -> protofilaments -> microtubule (13 protofilaments)

Question 13

lysosomes

Answer 13

• vesicles containing digestive enzymes
• bound by a single membrane
• keeps lysozymes (used to break material down) separate from the cytoplasm

Question 14

golgi apparatus

Answer 14

• a series of fluid- filled, curved and flattened sacs, with vesicles surrounding the edges
• sorts, processes and packages proteins and lipids
• produces lysosomes

Question 15

vesicles

Answer 15

• stores lipids processed by the Golgi
• transports them out of the cell

Question 16

ultrastructure of eukaryotic cells specific to plants

Answer 16

• cell wall
• chloroplast
• vacuole
• tonoplast

Question 17

primary cell wall

Answer 17

• consists of cellulose microfibrils that run in all directions, allowing the wall to grow and stretch, embedded in a matrix of complex polysaccharide molecules, which includes pectins and hemi- cellulose

Question 18

secondary cell wall

Answer 18

• consists of cellulose microfibrils that run parallel within each layer
• the inclusion of lignin makes it less flexible and less permeable to water
• provide additional protection to cells, and rigidity and strength to the plant
• has narrow pores through which fine strands of cytoplasm (plasmodesmata) pass

Question 19

chloroplast

Answer 19

• found in the cells of photosynthetic tissue of plants
• appears green due to the pigment chlorophyll

Question 20

vacuole

Answer 20

• contains cell sap, which is a solution of salts and sugars

Question 21

tonoplast

Answer 21

• a specialised membrane that surrounds the vacuole
• acts as a barrier between the fluid contents of the vacuole and the cytoplasm

Question 22

label

Answer 22

Question 23

magnification

Answer 23

how much bigger the image is compared to the original object

Question 24

resolution

Answer 24

how far apart two points can be before they are seen as one

Question 25

types of microscopes

Answer 25

- optical - scanning electron - transmission electron

Question 26

optical microscope

Answer 26

- a beam of light is shone through the object - an objective lens and an eyepiece lens magnifies the sample - magnification = 1500 x - resolution = 200 nm

Question 27

scanning electron microscope

Answer 27

- a beam of electrons scans over the surface of the sample, producing a 3D image - magnification = 50,000 x - resolution = 0.1 nm

Question 28

transmission electron microscope

Answer 28

- a beam of electrons is transmitted through the object, producing a 2D image - a very thin sample must be used - magnification = 100,000 - 500,000 x - resolution = 0.1 nm

Question 29

all microscopes give

Answer 29

artefacts - things observed due to preparative techniques etc stains

Question 30

advantages of electron microscope

Answer 30

- higher resolutions and magnifications can be achieved

Question 31

disadvantages of electron microscopes

Answer 31

- the sample must be placed in a vacuum, so living things can’t be magnified - very expensive and not portable - produces only black and white images

Question 32

importance of staining specimens in microscopy

Answer 32

- staining is the samples is required for both light and electron microscopes - it provides contrast between the organelles and the cytoplasm, allowing structures to be observed

Question 33

stains used on electron microscopes

Answer 33

- stained by heavy metals which reflect electrons

Question 34

stains used in light microscopes

Answer 34

- methylene blue - acetocarmine - haematoxylin