Biology Unit 1 Module 1

Front 1

Why did Hooke use the term 'cell'?

Back 1

In observing thin sections of cork, Hooke saw that the sections were made of a number of repeating, small, fairly rectangular spaces. These had the appearance of the shape of rooms in which monks lived. These rooms were called cells.

Front 2

Explain why enlarging a photograph taken with a light microscope does not show more detail.

Back 2

Magnification on its own does not increase the level of detail seen - this is dependent on the resolution, which is limited by the wavelength of light used in the microscope.

Front 3

Draw up a table to show each of the following measurements in metres (m), millimetres (mm) and micrometres (ɥm): 5ɥm, 0.3m, 23mm and 75ɥm.

Back 3

5ɥm = 0.005mm and 0.000005m

0.3m = 300000ɥm and 300mm

23mm = 23000ɥm and 0.023m

75ɥm = 0.075mm and 0.000075m

Front 4

The length of a nucleus is 3.2 epu. At x100 magnification, 1 epu = 10ɥm. How long is the nucleus (ɥm)?

Back 4

32ɥm

Front 5

The length of the same nucleus is 13 epu. At x400 magnification, 1 epu = 2.5ɥm. How long is the nucleus (ɥm)?

Back 5

32.5ɥm

Front 6

Calculate the actual size of a squamous epithelial cell in ɥm (to 3 significant figures) with a magnification of x1200 and image size of 5cm.

Back 6

41.6ɥm (3sf)

Front 7

If a nucleus measures 100mm on a diagram, with a magnification of x10,000, what is the actual size of the nucleus?

Back 7

10ɥm

Front 8

Calculate the magnification of a cell with an actual diameter of 5ɥm and measured as 25mm.

Back 8

x5000

Front 9

Calculate the actual size of a mitochondrion with magnification x18,500 and measured as 56mm.

Back 9

3ɥm

Front 10

A plant cell is 40ɥm in length. How long is its image when magnified x3000?

Back 10

120mm

Front 11

An animal cell is 60mm long when viewed x4000. What is the cell's actual length?

Back 11

15ɥm

Front 12

Suggest why light microscopes are so useful in biology.

Back 12

The light microscope is easy to use and can be used to observe living cells such as single-celled organisms. It can also be used to observe the arrangements of tissues in organisms.

Front 13

Explain the advantages of using the transmission and scanning electron microscopes to study cell structure.

Back 13

High resolution; so that details of cell structure can be seen e.g. membranes, organelles such as ribosomes, mitochondria and endoplasmic reticulum.

Front 14

Why do sections of tissue need to be cut into thin slices for examination under a microscope?

Back 14

Light cannot penetrate thick slices of tissues, so no detail would be seen.

Front 15

Explain why samples of biological material are stained before viewing in the light and electron microscopes.

Back 15

Most biological material is transparent; gives contrast to material.

Front 16

Describe the limitations of the light microscope.

Back 16

Low resolution so cannot magnify much above x1500 and still give a clear image.

Front 17

List the similarities and differences between light and electron microscopes.

Back 17

Both are microscopes and so enable us to see a magnified image of a small object. Both use a radiation source passed through the specimen; the radiation beam is focused using lenses. The radiation passed through the specimen is used to generate an image.

LM's are easier to use, portable and can be used to observe living specimens. To use EM's requires a great deal of skill and training. Preparation of specimens is difficult and the specimen has to be placed in a vacuum. It is not possible to observe living specimens. It is not possible to see colours of an electron micrograph - although colour can be added to give a false colour electron micrograph. Electron microscopes have much greater resolution and so can give greater magnification whilst giving a clear image.

Front 18

Describe the main limitations of the electron microscope.

Back 18

The inability to observe living material and the preparation processes required to observe specimens are the main limitations of the electron microscope.

Front 19

Explain why both light and electron microscopes are used widely in biology.

Back 19

Both types of microscope are used widely because they can give different information about living things. Although electron microscopes have greater resolution and magnification, they cannot be used to observe living cells and tissues. The light microscope gives us good detail of living processes in cells. The magnification of the electron microscope has allowed us to investigate the internal components of cells in great detail.

Front 20

List the characteristics of living things and describe how the organelles allow cells to show those characteristics.

Back 20

Movement: the cytoskeleton includes contractile proteins; cilia and undulipodia are also capable of movement.

Respiration: mitochondria are responsible for generating ATP in cellular respiration,

Sensitivity: some of the proteins made in the cell are packaged in the Golgi apparatus and placed on the cell surface membrane. Such proteins may act as sensors, for example to detect nutrient molecules in the surroundings.

Growth: this requires energy and therefore needs mitochondria. It also requires nutrients, brought into the cell, which can be moved around in vesicles.

Reproduction: making new cells requires instructions - these are stored in the nucleus.

Excretion: waste products need to be moved out of the cell, many of these can be moved out of the cell in vesicles

Nutrition: cells need nutrients to provide for their energy and growth needs, nutrients can be moved around cells in vesicles. Nutrients in the cell can be digested in lysosomes.

Front 21

Suggest why:

(a) chloroplasts are moved around plant cells

(b) white blood cells need to be able to move.

Back 21

(a) to gather maximum sunlight energy or to avoid being damaged by excess UV light(b) to detect and take up foreign molecules and invading microorganisms in the blood

Front 22

What type of cells in plants are animas would contain extensive Golgi apparatus?

Back 22

Cells that are responsible for the production of enzymes, hormones or growth regulators. Hormones and growth regulators require processing and packaging, for export, in the Golgi apparatus.

Front 23

Suggest why muscle cells contain a lot of mitochondria, whereas most fat storage cells do not.

Back 23

Muscle contractions require a lot of energy in the form of ATP, whereas fat storage cells have very low energy requirements. (Fat cells that store brown fat have many mitochondria, as these cells use their fat to generate heat energy.)

Front 24

Which cells in a plant are the ones that contain most chloroplasts?

Back 24

The cells in the leaf called palisade mesophyll cells.

Front 25

List these organelles in order of their size: nucleus, ER, mitochondrion, chloroplast, lysosome, ribosome, centriole.

Back 25

Nucleus, chloroplast, mitochondrion, ER, centriole, lysosome, ribosome

Front 26

Which of these organisms would you expect to find in 1. a palisade cell and 2. an enzyme-secreting palisade cell?

Mitochondria, chloroplast, nucleus, nucleolus, ribosome, RER, SER, Golgi, lysosome, centriole, cilia and undulipodia

Back 26

Both cells: nucleus, nucleolus, Golgi, mitochondria, RER, SER, ribosomes.

Only in 1: chloroplasts

Only in 2: lysosomes

Front 27

State 4 ways in which the structure of a eukaryotic cell differs from that of a prokaryotic cell.

Back 27

Among others: eukaryotic cell has: nucleus, mitochondria, Golgi apparatus, ER. Eukaryotic cell does not have plasmids, pili, flagellum or mesosomes.

Front 28

Define the term 'division of labour'.

Back 28

The sharing of tasks that need to be performed between specialists in each of the tasks. In cells, different organisms perform different functions. Each function is performed well by the organelle responsible, and the organelle performing its function contributes to the overall life of the cell.

Front 29

Explain how division of labour occurs in plant and animal cells.

Back 29

Organelles carry out different function within the cell. There are many examples in the spread.

Front 30

List all the features that prokaryotic and eukaryotic cells have in common.

Back 30

A cell surface membrane made of phospholipids, instructions in the form of DNA, ribosomes, cytoplasm, both can perform all the characteristics of living things.

Front 31

List the differences between prokaryotic and eukaryotic cells.

Back 31

Prokaryotic cells are much smaller, they do not have any internal membranes and so do not have a nucleus, mitochondria, chloroplasts, ER or lysosomes. Prokaryotic ribosomes are smaller.

Front 32

Mitochondria and chloroplasts contain small loops of DNA. They also contain ribosomes that are the same size as prokaryotic ribosomes. Suggest an explanation for these features.

Back 32

It is thought that chloroplasts and mitochondria have evolved from prokaryotic cells, and that the DNA and ribosomes they retain are derived from this evolution. This is known as the endosymbiont theory.

Front 33

Explain why membranes are described as fluid mosaic.

Back 33

Phospholipid bilayer is liquid; proteins are dispersed within the bilayer like moveable mosaic tiles.

Front 34

Why do we describe cell membranes as partially permeable rather than semi-permeable?

Back 34

Different membranes are permeable to a variety of substances and impermeable to a variety of other substances. Semi-permeable suggests 'half-permeable', which is unlikely to be the case in any membrane.

Front 35

Why can phospholipid molecules in a bilayer move only in the plane of the bilayer?

Back 35

The phosphate head group cannot pass through the hydrophobic region in the centre of the bilayer.

Front 36

Why do muscle cells need to be able to take up glucose rapidly?

Back 36

To support rapid respiration in order to supply ATP for contraction.

Front 37

Describe the distribution of membranes within animal and plant cells.

Back 37

Cell surface membrane, membranes of nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria and (in plants) chloroplasts and the membrane around the large vacuole.

Front 38

Explain how phospholipids and proteins influence the permeability of a cell surface membrane.

Back 38

Phospholipids allow small molecules (water, carbon dioxide, oxygen) and fat-soluble molecules to pass through, but not ions or larger water-soluble molecules. Proteins form channels and carriers to allow movement of ions and polar molecules that cannot pass through the phospholipid bilayer.

Front 39

If a protein spans the membrane, what property must the part of the protein embedded in the central part of the bilayer have?

Back 39

It must be constructed from amino acids with hydrophobic R-groups.

Front 40

What types of molecules are likely to be involved in:

(a) cell signalling and recognition?

(b) allowing small charged molecules to pass through the cell surface membrane?

(c) driving metabolic reactions?

Back 40

(a) Externally placed proteins and glycoproteins(b) Transmembrane protein pores (channels)(c) Enzymes, which are proteins

Front 41

What would happen to beetroot cell membranes if the temperature continued to increase beyond leaky membranes?

Back 41

Eventually the membrane would rupture and break down completely.

Front 42

Explain why cells need receptors to insulin, adrenaline and glucagon on the cell surface membrane, rather than inside the cytoplasm.

Back 42

These are water-soluble molecules that cannot cross the cell surface membrane.

Front 43

Name two target tissues for insulin.

Back 43

Liver cells and muscle tissue cells (and most cells, as it can increase glucose uptake and rate of respiration in many cells).

Front 44

Explain how some drugs can mimic the effects of hormones and neurotransmitters or block their actions.

Back 44

The drugs have shapes complementary to the shapes of the receptors.

Front 45

Suggest how flu viruses infect human cells of the respiratory tract.

Back 45

They are able to attach (by their surface antigens) to a normal cell surface membrane protein receptor found in these cells.

Front 46

Botulinum toxin binds to the ends of nerves and prevents them from releasing chemicals that normally cause muscles to contract. There are eight different botulinum toxins, some stronger than others. Suggest why some of the toxin molecules are more potent than others.

Back 46

Different toxins will have slightly different shapes, and so will attach more or less strongly to their target membrane proteins.

Front 47

List two substances that diffuse through a cell surface membrane in a plant cell of a lead and explain how the direction of diffusion will change in daylight compared with darkness.

Back 47

Carbon dioxide will diffuse into photosynthesising plant cells when there is light, oxygen will diffuse out of the plant cell at this time. Some of the oxygen produced during photosynthesis will be used for respiration, but the rate of photosynthesis will exceed that of respiration for much of the day. In darkness, carbon dioxide will diffuse out of the cell because respiration continues, so oxygen will diffuse into the cell at this time.

Front 48

Explain why a single-celled organism such as Amoeba can gain enough oxygen for its respiration through simple diffusion across its membrane.

Back 48

An amoeba is very small, so has a large surface-area-to-volume ratio. All the amoeba's cell contents are close to the oxygen supply in the surrounding water and so diffusion is sufficient for the organism's needs.

Front 49

Explain why carbon dioxide diffuses through phospholipid layers, but glucose does not.

Back 49

Both molecules are polar, but carbon dioxide is much smaller and can pass between phospholipids, glucose is too large to be able to do this.

Front 50

Give a definition for facilitated diffusion. Compare and contrast simple diffusion and facilitated diffusion.

Back 50

Both simple and facilitate diffusion involve the movement of materials from a place of higher concentration to a place of their lower concentration. Facilitated diffusion requires a protein channel to 'allow' the diffusion to take place. Simple diffusion is where molecules are small enough, or are not charged, and can diffuse through the lipid bilayer. Large, fat-soluble molecules can also pass by simple diffusion through the lipid bilayer.

Front 51

State three ways in which active transport differs from facilitated diffusion.

Back 51

Active transport uses carrier proteins (not channel proteins); uses energy in the form of ATP; moves substances against their concentration gradient.

Front 52

Explain why root hair cells have mitochondria.

Back 52

Mitochondria provide energy for active transport of ions.