Basic Components of Living Systems

Question 1

How does a light microscope work?

Answer 1

Light shines up through the sample being observed and through two lenses (objective and eyepiece). Each lens magnifies the image; the combined effect of the two lenses can increase an image by up to 2000 times its actual size

Question 2

What is magnification?

Answer 2

Magnification is the extent to which the actual size of an object is enlarged into the image seen through a microscope

Question 3

What is resolution?

Answer 3

• Resolution is the extent to which two objects can be distinguished as separate structures. More detail can be seen at higher resolutions
• The shortest distance between to objects that are still seen as separate structures

Question 4

How to calculate magnification?

Answer 4

Size of image/actual size of object

Question 5

How to calibrate a microscope

Answer 5

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Question 6

Light microscope

Answer 6

• Magnification: up to x2000
• Resolution (nm): 200
• Benefits: inexpensive, short preparation time, can see colour, can observe living material
• Disadvantages: limited magnification and resolution

Question 7

Transmission electron microscope (TEM)

Answer 7

• How does it work?: electron beams pass through the specimen
• Magnification: up to x500,000
• Resolution (nm): 0.5
• Benefits: high magnification and resolution, enables intracellular details to be observed
• Disadvantages: expensive, complex preparation of samples, black and white images, artefacts can be introduced during preparation

Question 8

Scanning electron microscope (SEM)

Answer 8

• How does it work?: electrons are reflected back from the specimen and detected
• Magnification: up to x100,000
• Resolution (nm): 3-10
• Benefits: high magnification and resolution, 3D images
• Disadvantages: expensive, complex preparation of samples, black and white images, artefacts can be introduced during preparation

Question 9

Confocal laser scanning microscope (CLSM)

Answer 9

• Uses laser light to scan a specimen
• Light is absorbed by fluorescent chemicals and radiated back from the specimen
• Although the resolution of these microscopes is poor compared to electron microscopes, they have two benefits: 3D images are produced, they are non-invasive (which allows living tissue to be observed)

Question 10

What is an artefact?

Answer 10

An artefact is something visible in a microscope that is not a natural part of the specimen (e.g. structural distortion created during preparation)

Question 11

Examples of eukaryotes

Answer 11

Animals, plants, fungi, and protoctista

Question 12

What is the ultrastructure of the cell?

Answer 12

The ultrastructure of the cell is the fine detail that can be observed only by using an electron microscope

Question 13

Nucleus

Answer 13

• Function: contains genetic information
• Key features: surrounded by a nuclear envelope (containing pores); contains chromatin (DNA + histone proteins), which condenses to form chromosomes, contains a nucleolus (which produces rRNA)

Question 14

Mitochondria

Answer 14

• Function: ATP production through aerobic respiration

- Key features: double membrane (the inner membrane folds to form cristae); internal fluid is called the matrix

Question 15

Lysosomes

Answer 15

• Function: breaking down waste (e.g. old organelles)

- Key features: specialised vesicles (membranous sacs), containing hydrolytic enzymes

Question 16

Smooth endoplasmic reticulum

Answer 16

• Function: lipid and carbohydrate synthesis

- Key features: flattened membrane-bound sacs (cisternae)

Question 17

Rough endoplasmic reticulum

Answer 17

• Function: protein synthesis

- Key features: cisternae bound to ribosomes (which are made of RNA; ribosomes can also appear loose in cytoplasm)

Question 18

Golgi apparatus

Answer 18

• Function: modifying proteins and packaging them into vesicles
• Key features: flattened sacs (similar to smooth ER)

Question 19

Cytoskeleton

Answer 19

• Function: maintaining cell shape, control of cell movement and organelle movement in cells, compartmentalisation of organelles
• Key features: microfilaments (made from actin) control cell movement and cytokinesis; microtubules (made from tubulin) regulate shape and organelle movements, they form centrioles and spindle fibres

Question 20

Flagella and cilia

Answer 20

• Function: flagella enable cell movement, cilia move substances across cell surfaces
• Key features: both compromise a cylinder containing 11 microtubules (nine in a circle and two in the centre), flagella are longer than cilia

Question 21

Ribosomes

Answer 21

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Question 22

Cellulose cell wall

Answer 22

• Found in plants
• A strong barrier on the outside of the cell membranes. It is composed of a polysaccharide called cellulose
• Provides shape and rigidity

Question 23

Large, permanent vacuole

Answer 23

• Found in plants
• A large, central sac (surrounded by a membrane known as a tonoplast). It principally contains water
• Increases turgor (i.e. the extent to which cells are filled with water)

Question 24

Chloroplasts

Answer 24

• Found in plants
• A organelles containing fluid (stroma) and a network of membranes (thylakoids, which are stacked as grana)
• The organelle responsible for photosynthesis

Question 25

What are fungi cell walls made of?

Answer 25

Chitin

Question 26

What are bacterial cell walls made of?

Answer 26

Peptidoglycan

Question 27

Prokaryotic cells (unicellular)

Answer 27

• No membrane-bound organelles
• One main molecule of DNA (circular and found naked in the cytoplasm), additional DNA can be found in plasmids
• Has a cytoskeleton (but comprising of different proteins to the eukaryotic cytoskeleton)
• 70S ribosomes (size)
• Flagella are sometimes present, but with a different structure to eukaryotes
• Cell wall of peptidoglycan (murein), a polymer of sugars and amino acids
• Asexual reproduction (binary fission)

Question 28

Eukaryotic cells (multicellular)

Answer 28

• Has membrane-bound organelles
• Linear (chromosomes) DNA and associated with histone proteins in a nucleus, additional DNA found in mitochondria and chloroplasts
• Has a cytoskeleton
• 80S ribosomes (size)
• Cilia and flagella often present in animal cells
• Cell wall present in plant cells (made of cellulose) and fungi (made of chitin)
• Sexual or asexual reproduction