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Biology AS (OCR) Unit 1 > Module 1- Cells > Flashcards

Module 1- Cells Flashcards

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1
Q

Define Magnification.

A

Magnification is the degree to which the size of an image is larger than the object itself. Numerically it is the image size divided by actual size measured using the same units.

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2
Q

Define Resolution.

A

Resolution is the degree to which it is possible to distinguish between two objects that are very close together. The higher the resolution the greater the detail.

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3
Q

What is the maximum magnification of a light microscope.

A

Most light microscopes are capable of magnification up to x1500.

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4
Q

What is the maximum resolving power when using a light microscope?

A

The maximum resolving power using light in 200nm.

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5
Q

When examining two objects closer together than 200nm with a light microscope what problem will occur?

A

If two object are closer than 200nm they will be seen as one object, this is because particles can be seen if they are further apart than half the wavelength of light.

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6
Q

What is one disadvantage of the Light Microscope?

A

Light Microscopes can’t be used to give detailed information about the internal structure of a cell.

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7
Q

How do you calculate the total magnification of any specimen?

A

The total magnification of any specimen is given by multiplying the objective magnification by the eyepiece magnification.

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8
Q

On a light microscope how many lenses are present?

A

Usually four objective lenses are present x4, x10, x40, and x100 (oil immersed).

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9
Q

How much does the eyepiece lens on a light microscope usually magnify by?

A

x10.

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10
Q

Why is it important to prepare some specimens before viewing them under a light microscope?

A

You can view some specimens directly. However alot of biological material is not coloured so you cant see the details. Also some material distorts when you try to cut it.

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11
Q

What happens during the process of staining?

A

Coloured stains are chemicals that bind on or in the specimen. This allows the specimen to be seen. Some stains bind to specific cell structures.

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12
Q

Give an example of chemical and what it stains.

A

Acetic orecin stains DNA dark red.

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13
Q

What happens during the process of sectioning?

A

Specimens are embedded in wax. Thin sections are then cut without distorting the structure of the specimen. This is particularly useful in soft tissue.

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14
Q

What is the international unit for length (SI) ?

A

The international unit for length is the metre (m).

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15
Q

what is one micrometre equal to?

A

One micrometer (um) is a millionth of a metre (10-6)

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16
Q

How long are Animal Cells?

A

Animal cells are usually 20-40 um long.

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17
Q

Which is smaller the nanometre or the micrometre?

A

The nanometre is smaller as it is equal to 1/1000th of a micrometre.

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18
Q

what is the limit of resolution for an electron microscope?

A

The limitation of the resolving power is equal to 0.20 nm.

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19
Q

What does each unit on a stage micrometer equal?

A

The ruler is 1mm long with 100 equal divisions. Each division is 10um

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20
Q

What is the relationship between actual size, magnification, and image size.

A

actual size= image size/magnification.

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21
Q

Define Staining.

A

Staining in microscopy refers to any process that helps to reveal or distinguish different features. In light microscopy, stains may be colours or fluorescent dyes. In electron microscopy, they are metal particles or metal salts.

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22
Q

what are the two types of Electron Microscope?

A

Transmission Electron Microscope (TEM) & Scanning Electron Microscope (SEM).

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23
Q

Explain how a TEM works.

A

The electron beam passes through a thin sample.

Electrons pass through the denser parts of the sample less easily, giving contrast.

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24
Q

What is the highest magnification possible with a TEM?

A

x500 000

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25
Q

Using a TEM is the final image produced 2D or 3D?

A

It is a 2D image.

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26
Q

Explain how an SEM works.

A

The electron beam is directed onto a sample. Electrons don’t pass through the specimen.
Electrons are bounced off the sample.

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27
Q

What is the highest Magnification possible with SEM

A

x100 000

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28
Q

Give some advantages of the electron microscope.

A

The resolution is 0.20 nm (x1000 more than in the light microscope).
Produces detailed images of the organelles inside cells.
Can reveal detail of contours and tissue arrangements.

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29
Q

Limitations of electrons microscopes.

A

Electron beams are deflected by molecules in the air- samples must be placed in a vacuum.
They are extremely expensive.

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30
Q

Define Cytoskeleton.

A

the cytoskeleton refers to the network of protein fibres found within cells that gives structure and shape to the cell, and also moves organelles around inside cells.

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31
Q

Define Ultrastructure.

A

The detail of the inside of the cells, as revealed by the electron microscope, is termed the cells ultrastructure.

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32
Q

Name the organelles which are surrounded by membranes.

A

The nucleus, Endoplasmic reticulum, Golgi apparatus, Mitochondria, Chloroplasts and Lysosomes.

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33
Q

Name the Organelles without membranes.

A

Ribosomes, Centrioles

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34
Q

At what magnification is a cell membrane visible.

A

Membranes are visible in the TEM at magnifications of x100 000 as two dark lines separated by a clear space.

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35
Q

What is the Fluid-Mosaic model?

A

The fluid-mosaic model is the current model used by biologists to explain the structure of the plasma membranes in cells.

36
Q

Name 5 functions of phospholipids.

A

form a bilayer that acts as a barrier between cytoplasm and cell exterior: are fluid so components can move within the membrane: permeable to non polar molecules such as oxygen and small polar molecules such a water: impermeable to large polar molecules such as sugars.

37
Q

Name 3 functions of Cholesterol.

A

Stabilises the phospholipid bilayer by binding to polar heads and non polar tails. Controls fluidity by preventing phospholipids solidifying at low temperatures and becoming too fluid at high ones.Reduces permeability to water, ions…

38
Q

Name 2 functions of Proteins.

A

There are transmembrane proteins acting as channels and carriers. They are receptors for chemicals made by other cells e.g. hormones.

39
Q

Name the functions of Glycoproteins and Glycolipids.

A

Acts as receptors for signalling molecules, acts as cell surface markers that identify the cells (known as antigens). They are involved in cell adhesion.

40
Q

Explain why membranes are partially permeable.

A

Membranes are partially permeable because some substances can pass through but others do not. Membranes are SELECTIVE.

41
Q

What is the permeability of a membrane determined by?

A

The permeability of a membrane is determined by the phospholipids and the proteins.

42
Q

What is the function for membranes within cells?

A

Dividing the cell into compartments where functions can occur more efficiently. To isolate potentially harmful enzymes in lysosomes. Surround vesicles that transport molecules between parts of the cell.

43
Q

Explain why membranes are described as fluid mosaic.

A

Membranes are described as fluid mosaic because phospholipids are liquid and the membrane is like a layer of thin oil. Also, it is made up of many components with the phospholipids acting as cement holding everything together.

44
Q

What is the function of Mitochondria?

A

Aerobic respiration. (They have a highly folded membrane to give a large surface area for enzymes).

45
Q

What is the function of Chloroplasts?

A

Photosynthesis. (Grana made from stacks of membranes to give them large surface area for chlorophyll and other pigments).

46
Q

What is the function of the Nucleus?

A

Contains genetic informations in DNA of chromosomes. ( Separated from cytoplasm by the nuclear envelope - porous for communication).

47
Q

What is the function of the Nucleolus?

A

Production of ribosomes (dark staining area in the nucleus).

48
Q

What is the function of Ribosomes?

A

Amino acids assemble to make proteins. (On rough endoplasmic reticulum or free in the cytoplasm)

49
Q

What is the function of Rough Endoplasmic Reticulum?

A

Site for ribosomes, transports proteins to the Golgi Apparatus.

50
Q

What is the function of the Smooth Endoplasmic Reticulum?

A

Makes triglycerides (fats), phospholipds and cholesterol.

51
Q

What is the function of the Golgi Apparatus?

A

Modifies and packages proteins, makes secretory vesicles and lysosomes.

52
Q

What is the function of Lysosomes?

A

Contains enzymes for destroying worn-out parts of the cell

53
Q

What is the function of the Centriole?

A

Assembles microtubules for the cytoskeleton, and to form spindle to move chromosomes when the nucleus divides.

54
Q

What is the function of Cilia?

A

Moves Liquids or materials along tubes.

55
Q

What is the function of Undulipodia ?

A

Moves sperm cells and gametes of some plant cells.

56
Q

Why is Diffusion considered to be a passive process?

A

Diffusion occurs passively- no ATP is required by the cell to move substances across the membrane because they move down their concentration gradient.

57
Q

Osmosis is the diffusion of what molecule across a membrane

A

Water molecules.

58
Q

Define Water Potential.

A

Water potential is the tendency for water molecules to move from one place to another.

59
Q

Define Osmosis.

A

Osmosis is the movement of water molecules from a region of high potential, to a region of low potential across a partially permeable membrane.

60
Q

What are the factors that affect Osmosis?

A

The amount of water present in the cytoplasm and in the exterior environment
The concentration of solutes, such as ions and sugars, on either side of the cell surface membrane.
The presence of aquaporins in membranes.
The pressure exerted on cell contents by the cell wall.

61
Q

Why is facilitated diffusion also essential to cells?

A

Many molecules that cells need are too large to pass between the phospholipid bilayer. There may also be charged particles unable to go through the hydrophobic region .

62
Q

What are Channel proteins?

A

Channel proteins are transmembrane proteins that form tunnels or pores through the bilayer for water soluble molecules. Some channels are open all the time and others are triggered open.

63
Q

What are Carrier proteins?

A

Carrier proteins change shape to help move molecules into or out of the cell. Molecules bind to the protein, which stimulates the protein to change its overall shape so allowing the molecule to pass through the membrane.

64
Q

What are the two forms of bulk transport?

A

Endocytosis and Exocytosis.

65
Q

Define Endocytosis.

A

Endocytosis- substances packaged by the Golgi apparatus are delivered to the cell surface in vesicles, which fuse with the cell surface membrane to push out their contents.

66
Q

Define Exocytosis.

A

Exocytosis- some cells take up large molecules (such as bacteria) by enclosing them inside vesicles or vacuoles formed by the cell surface membrane.

67
Q

State three ways in which active transport differs from facilitated diffusion

A

Active transport uses carrier proteins (instead of channel proteins) It uses energy in the form of ATP and moves substances against their concentration gradient.

68
Q

What are the four main stages of mitosis?

A

Prophase, Metaphase, Anaphase and Telophase.

69
Q

Explain what happen during Prophase stage of a mitotic cell.

A

The DNA in chromosomes is packaged. Chromosomes shorten and thicken. This makes it easy for the cell to move chromosomes around. The chromosomes are now condensed and each chromosome has two chromatids. The nuclear envelope begins to break up into small pieces and disperse throughout the cell.

70
Q

Explain what happens during Metaphase stage of a mitotic cell.

A

Chromosomes come to the middle of the cell. Centrioles (where present) organise microtubules into spindle that stretches across the cell. Chromosomes are attached to the spindle at their centrometre.

71
Q

Explain what happens during Anaphase.

A

Chromatids break apart at the centrometre and are pulled apart by the spindle towards the poles. Once separated, the chromatids are chromosomes.

72
Q

Explain what happens during Telophase.

A

Nuclear envelopes reform around each group of the chromosomes at either end of the cell. The chromosomes uncoil.

73
Q

Define differentiation.

A

The production of erythrocytes(red blood cells) and neutrophils derived from stem cells in bone marrow, and the production of xylem vessels and phloem sieve tubes from cambium.

74
Q

What changes during differentiation?

A

Number of organelles, Shape of the cell, and some of the contents inside the cell.

75
Q

Where are undifferentiated cells found?

A

Undifferentiated cells are found in the bone marrow.

76
Q

What do all cells have the potential to become?

A

All cells have the potential to become red or whit blood cells.

77
Q

Describe and explain how Erythrocytes are specialised cells.

A

Erythrocytes lose their nucleus, mitochondria, Golgi and rough ER. They are packed full of haemoglobin molecules for maximum oxygen transportation.

78
Q

What is the function of an Erythrocyte?

A

Erythrocytes transport oxygen from lungs to tissues.

79
Q

Describe and explain how sperm cells are specialised due to organelle content.

A

Energy for movement of the undulipodium (flagellum) is generated by the many mitochondria present within the cell.
The sperm head contains a specialised lysosome called an acrosome, this release enzymes onto the outside of the egg to help the sperm to penetrate and fertilise the egg.

80
Q

Describe and explain how sperm cells are specialised due to their shape.

A

Sperm cells are very small, long and thin helping with movement.
Single long undulipodium helps to propel the cell up the uterine tract to reach the egg.

81
Q

What are the four main types of animal tissue.

A

Epithelial (lining and layers)
connective (cartilage, bone, and blood.)
muscle (contract and move)
Nervous (conduct impulses)

82
Q

Name the features of squamous epithelial tissue that makes it specialised to do a particular function.

A

Its found in lining and layers.
flattened cells make a thin and smooth surface.
Fluids pass easily over the tissue.
it has a short diffusion pathway.
Attatched to connective tissue by basement membrane
Found blood vessels and alveoli..

83
Q

Name the features of ciliated epithelial tissue that makes it specialised to do a particular function.

A 
Column shape cells.
Inner surface of tubes.
Cell surface exposed to lumen covered in projections called cilia.
Rhythmic waves move egg along oviduct.
Often produce mucus.
84
Q

Define an organ.

A

A collection of tissues that work together to carry out a specific function.

85
Q

Name 4 Plant Organs.

A

Flower, Stem, Leaves and Roots.

Biology AS (OCR) Unit 1 (2 decks)

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