2.1.1 Cell structure Flashcards

1
Q

Two types of microscopes

A

Light microscope and electron microscope

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2
Q

Light microscope images allow the observation of …

A

Cell shape and larger internal structures

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3
Q

Advantages of light microscopes:

A

they are small and relatively cheap,
specimen preparation can be straightforward enough to perform in a school laboratory,
they can be used to produce colour images,
they allow the observation of living specimens

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4
Q

Electron microscopes can be used to observe …

A

Small structures inside cells

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5
Q

Limitations of electron microscopes:

A

They are very large and expensive,
Specimens must be prepared using a highly complex process,
Specimens must be viewed in a vacuum meaning that live specimens cannot be observed,
Images are always black and white though they can be artificially coloured during processing

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6
Q

Two types of electron microscope:

A

Transmission electron microscopes (TEMs)
and scanning electron microscopes (SEMs)

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7
Q

How do TEMs create an image?

A

TEMs use electromagnets to transmit a beam of electrons through a specimen; denser parts of the specimen absorb more electrons, meaning that denser parts appear darker on the final image

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8
Q

How do SEMs create an image?

A

SEMs pass a beam of electrons across the surface of a specimen and then detect the rate at which the electrons bounce back

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9
Q

TEMs produce images that:

A

Are high-resolution,
allow the internal structures within cells and within organelles to be seen,
are two-dimensional

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10
Q

SEMs produce images that:

A

Are three-dimensional,
show the surface of specimens,
SEMs have a lower maximum resolution than TEMs

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11
Q

How to prepare a slide using a liquid specimen:

A
  1. Add a few drops of the sample to the slide using a pipette
  2. Cover the liquid/smear with a cover slip and gently press down to remove air bubbles
  3. Wear gloves to ensure there is no cross-contamination of foreign cells
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12
Q

How to prepare a microscope slide using a solid specimen:

A
  1. Take care when using sharp objects and wear gloves to prevent the stain from dying your skin
  2. Use scissors to cut a small sample of the tissue
  3. Peel away or cut a very thin layer of cells from the tissue sample to be placed on the slide (using a scalpel or forceps)
    The tissue needs to be thin so that the light from the microscope can pass through
  4. Apply a stain
  5. Gently place a cover slip on top and press down to remove any air bubbles
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13
Q

Why does staining in light microscopy make structures within the specimen visible?

A

The dyes used absorb specific colours of light while reflecting others

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14
Q

What is differential staining in light microscopy?

A

Certain tissues absorb certain dyes, which dye they absorb depends on their chemical nature. Specimens or sections are sometimes stained with multiple dyes to ensure the different tissues within the specimen show up

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15
Q

What happens to a stained specimen using a TEM?

A

The dyes used for staining cause the tissues to show up black or different shades of grey

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16
Q

Why are heavy-metal compounds commonly used as dyes in electron microscopy?

A

Because they absorb electrons well

17
Q

Magnification calculation:

A

magnification = size of image ÷ size of real object

18
Q

Magnification can be defined as:

A

The number of times larger an image is than the actual object

19
Q

Resolution can be defined as:

A

The ability to distinguish separate points on an image as two separate objects

20
Q

How are light microscopes limited by wavelength of light?

A

As light passes close to physical structures it is diffracted, meaning that light waves spread out
The closer the structures are to each other, the more the light waves overlap each other as they are diffracted
Points that are closer together than half the wavelength of visible light cannot be clearly distinguished from each other

21
Q

Why is resolution higher in electron microscopes?

A

Because electrons have a smaller wavelength than visible light
The objects past which the electrons travel can therefore be much closer together before the diffracted beams overlap

22
Q

Eukaryotic cell definition-

A

A type of cell that contains a nucleus along with membrane bound organelles

23
Q

Prokaryotic cell definition-

A

A type of cell that does not contain any membrane bound organelles or a nucleus

24
Q

Nucleus definition-

A

An organelle found in eukaryotic cells that stores the genetic information of the cell
as chromosomes and is surrounded by a membrane called the nuclear envelope

25
Q

Nuclear envelope definition-

A

A double membrane that surrounds the nucleus, and contains nuclear pores

26
Q

Purpose of nuclear pores-

A

Allow molecules to move into and out of the nucleus

27
Q

Nucleolus definition-

A

A structure found inside the nucleus that contains proteins and RNA and is involved in synthesizing new ribosomes

28
Q

Mitochondrion definition-

A

An organelle found in eukaryotic cells that is the site of aerobic respiration

29
Q

Structure of mitochondria-

A

Have a double membrane. The inner membrane is highly folded to form structures called cristae and the fluid interior is called the matrix. Also contain a small amount of DNA

30
Q

Vesicle definition-

A

Membranous sacs that have storage and transport roles, and consist of a single membrane with fluid inside

31
Q

Lysosomes definition-

A

Membrane-bound vesicles found in the cytoplasm that contain a hydrolytic
enzyme called lysozyme, and are responsible for breaking down waste material in cells

32
Q

Plasma membrane definition-

A

A semipermeable lipid bilayer studded with proteins that surrounds the
cell and many organelles

33
Q

Cytoskeleton definition-

A

A network of protein fibres found in the cytoplasm of eukaryotic cells used for structural support and intracellular transport

34
Q

What are the 3 components of the cytoskeleton?

A

Microfilaments, microtubules, intermediate fibres

35
Q

Microfilaments definition and function-

A

Contractile fibres made from the protein actin, responsible for cell movement and cell contraction during cytokinesis

36
Q

Microtubules definition and function-

A

Globular tubulin proteins polymerise to form tubes that are used to form a scaffold-like structure that determines the shape of the cell. They also act as tracks for the movement of organelles

37
Q

Intermediate fibres function-

A

Give mechanical strength to cells