Specification

Question 0

State the resolution and magnification that can be achieved by a light microscope, a transmission electron microscope and a scanning electron microscope.

Answer 0

Light microcope:
Resolution-0.2um (200nm)
Magnification-x1500

Transmission electron microscope:
Resolution-0.0001um (0.2nm)
Magnification-more than x1,000,000

Scanning electron microscope:
Resolution-0.005um (2nm)
Magnification-less than x1,000,000

Question 1

Explain the difference between magnification and resolution.

Answer 1

Magnification is how much bigger the image is than the specimen. Resolution is how well a microscope distinguishes between two points that are close together.

Question 2

Explain the need for staining samples for use in light microscopy and electron microscopy.

Answer 2

The beam of light or electrons passes through the specimen. An image is produced because some parts of the specimen absorb more light or electrons.

Sometimes the specimen is transparent, which makes it look white because the light rays or electrons pass straight through.

Stains (methylene blue/ eosin for light microscopes, heavy metals like lead for electron microscopes) are taken up by some parts of the specimen more than others. The contrast makes different parts show up, an image is produced because some parts are darker than others.

Question 3

Calculate the linear magnification of an image.

An insect is 0.5mm long. In a book, the picture is 8cm long. Calculate the magnification.

Answer 3

Magnification=new image(same unit)/ actual size of specimen (same unit)
x160

Question 4

What is the function and structure of the nucleus?

Answer 4

Functions:
It contains chromatin, which is made from proteins and DNA. DNA controls the cell’s activities. The pores allow substances, such as RNA, to move between the nucleus and the cytoplasm.
Structure:
A large organelle surrounded by a nuclear envelope, which contains many pores. The nucleus contains chromatin and often a nucleolus.

Question 5

What is the function and structure of the nucleolus?

Answer 5

Functions:
It produces ribosomes which leave the nucleus to take position on the rough ER.
Structure:
Inside the nucleus
Contains fibrillar and granular components

Question 6

What is the function and structure of the nuclear envelope?

Answer 6

Functions:
Allows exchange between the nucleus and the cytoplasm.
Structure:
A double membrane around the nucleus containing nuclear pores.

Question 7

What is the function and structure of the rough endoplasmic reticulum?

Answer 7

Function:
Folds and processes proteins that have been made at the ribosomes.
Structure:
A system of membranes enclosing a fluid-filled space. The surface is covered with ribosomes.

Question 8

What is the function and structure of the smooth endoplasmic reticulum?

Answer 8

Function:
Synthesises and processes lipids.
Structure:
A system of membranes enclosing a fluid-filled space.

Question 9

What is the function and structure of the Golgi apparatus?

Answer 9

Function:
It processes and packages proteins into vesicles. It also makes lysosomes.
Structure:
A group of fluid-filled, flattened sacs. Vesicles are often seen at the edges of the sacs.

Question 10

What is the function and structure of the ribosomes?

Answer 10

Function:
The site of protein synthesis.
Structure:
Very small, and is either free in the cytoplasm or attached to the rough endoplasmic reticulum.

Question 11

What is the function and structure of the mitochondria?

Answer 11

Function:
The site of aerobic respiration, where ATP is produced. They are very active and require a lot of energy.
Structure:
A double membrane bound organelle- the inner membrane is folded to form cristae to increase surface area inside the matrix. The matrix contains enzymes involved in respiration.

Question 12

What is the function and structure of the lysosomes?

Answer 12

Function:
Contains hydrolytic enzymes (digestive enzymes), which in a white blood cell, digest bacteria. These enzymes are kept separate from the cytoplasm by the membrane. They can be used to digest invading cells, or to break down worn out components of the cell.
Structure:
A round organelle surrounded by a membrane with no clear internal structure.

Question 13

What is the function and structure of the chloroplasts?

Answer 13

Function:
Contains chlorophyll, the site of photosynthesis, some parts happen in the grana, others in the stroma.
Structure:
A small, flattened structure found in plant cells, surrounded by a double membrane. It contains membranes called thylakoid membranes, which are stacked up in the chloroplast to form grana. Grana are linked together by lamellae. (lamellae are thin, flat pieces of thylakoid membrane).

Question 14

What is the function and structure of the plasma membrane?

Answer 14

Function:
A phospholipid bilayer, containing proteins, which regulates the movement of substances into and out of the cell. It has receptor molecules on it, which allow it to respond to chemicals like hormones.
Structure:
A membrane on the surface of animal cells and just inside the cell wall of plant cells. It’s made of lipids and proteins. These proteins include receptors, pores and enzymes.

Question 15

What is the function and structure of the centrioles?

Answer 15

Function:
Formed from a ring of microtubules which are used to grow the spindle fibres used in nuclear division to separate chromosomes.
Structure:
Small, hollow cylinders containing a ring of microtubules which are tiny protein cylinders.

Question 16

What is the function and structure of the flagella?

Answer 16

Function:
Microtubules inside the flagella contract to make the flagellum move. They are used to propel cells forward.
Structure:
They protrude from the plasma membrane. They are small, hair-like structures. In cross-section, they have an outer membrane and a ring of 9 pairs of protein microtubules inside, with a single pair in the middle.

Question 17

What is the function and structure of the cilia?

Answer 17

Function:
The microtubules within the cilia allow it to move, which is used by the cell to move substances along the cell’s surface.
Structure:
Small, hair-like structures found the the surface membrane of some animal cells. In cross-section they have an outer membrane and a ring of 9 pairs of protein microtubules inside, with a single pair in the middle.

Question 18

Outline the interrelationship between the organelles involved in the production and secretion of proteins (no detail of protein synthesis is required)

Answer 18

1. The ribosomes on the rough ER make proteins that are excreted or attached to the cell membrane. The free ribosomes in the cytoplasm make proteins that stay in the cytoplasm.
2. New proteins made at the rough ER are folded and processed (e.g. Sugar chains are added) in the rough ER.
3. In vesicles, proteins are transported from the ER to the Golgi apparatus.
4. At the Golgi apparatus, the proteins may undergo further processing (e.g. Sugar chains are trimmed or more are added).
5. The proteins enter more vesicles to be transported around the cell (e.g. Glycoproteins, found in mucus, move to the cell surface and are secreted).

Question 19

Explain the importance of the cytoskeleton

Answer 19

The cytoskeleton is a network of protein fibres running through the cell’s cytoplasm. In eukaryotic cells, the cytoskeleton is arranged as micro filaments and microtubules, providing mechanical strength to cells, aiding transport within cells and enabling cell movement.

1. The micro tubules and micro filaments support the cell’s organelles, keeping them in position.
2. They help to strengthen the cell and maintain it’s shape.
3. They’re responsible for the transport of materials within the cell (e.g. The movement of chromosomes during cell division)
4. They can cause the cell to move (e.g. Via the cilia and flagella by propelling the whole cell)

Question 20

Explain, in terms of surface area:volume ratio, why a multicellular organism needs specialised exchange surfaces and single-celled organisms do not

Answer 20

Organisms need to supply every cell with substances and remove waste products from every cell to avoid damaging itself, so multicellular organisms have a greater demand for exchange because of their larger volume.

1. In single-celled organisms, theses substances can diffuse directly into (or out of) the cell across the cell surface membrane.
2. In multicellular animals, diffusion across the outer membrane is too slow, for two reasons….
   - some cells are deep within the body- there’s a big distance between them and the outside environment.
   - Larger animals have a low surface area to volume ratio- it’s difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface.

Question 21

Describe the features of an efficient exchange surface, with reference to diffusion of oxygen and carbon dioxide across an alveolus.

Answer 21

1. A large surface area to increase the rate of diffusion:
   Many alveoli provide a large surface area for diffusion to occur across.
2. They’re thin, providing a short diffusion pathway across the gas exchange surface, which increases the rate of diffusion:
   The alveolar epithelium and capillary endothelium are each only one cell thick, giving a short diffusion pathway.
3. The organism maintains a steep concentration gradient of gases across the exchange surface, which increases the rate of diffusion:
   The alveoli have a good blood supply from capillaries, constantly taking away oxygen and bringing more carbon dioxide. Inspiration and expiration refreshes the air in the alveoli, keeping the concentration gradients high.

Question 22

Describe the features of the mammalian lung that adapt it to efficient gaseous exchange

Answer 22

1. Many alveoli, large surface area for diffusion.
2. Alveolar epithelium and capillary endothelium only 1 cell thick each, short diffusion pathway.
3. Alveoli blood supply, breathing in and out- concentration gradient.
4. Goblet cells, mucus traps microorganism and dust from reaching the alveoli.
5. Cilia beats mucus upwards towards throat, where it’s swallowed, preventing lung infections.
6. Elastic fibres in walls of trachea, bronchi, bronchioles and alveoli stretch then recoil when inspiring and expiring to help push the air out.
7. Smooth muscle in trachea, bronchi and bronchioles walls allow their diameter to be controlled (wider during exercise, less resistance to airflow-easier for air to move in and out).
8. Rings of cartilage in trachea and bronchi walls for support and flexibility, preventing collapse as the pressure drops when inspiring, and allowing movement

Question 23

Describe the functions of cartilage, cilia, goblet cells, smooth muscle and elastic fibres in the mammalian gaseous exchange system

Answer 23

Cartilage
Support and flexibility. Prevents trachea and bronchi collapsing during inspiration as pressure drops. Allows movement of neck.

Cilia
Beats mucus with trapped dust and microorganisms in the inhaled air, prevents them from reaching the alveoli.

Goblet cells
Secrete mucus, which trap microorganisms and dust from the inhaled air, stopping them from reaching the alveoli.

Smooth muscle
In the walls of trachea, bronchi and bronchioles, controlled diameter, wider=less resistance to air during exercise, easier to breath.

Elastic fibres
In walls of trachea, bronchi, bronchioles and alveoli. Stretched when breathing in, then recoiling when breathing out to push air out.

Question 24

Outline the mechanism of breathing (inspiration and expiration) in mammals, with reference to the function of the rib cage, intercostal muscles and diaphragm

Answer 24

Inspiration:

• Diaphragm contracts, becomes flatter, pushes digestive organs down.
• External intercostal muscles contract, raising ribs.
• Volume of chest cavity increases.
• Pressure in chest cavity drops below atmospheric pressure.
• Air moves into lungs.

Expiration

• Diaphragm relaxes, pushed up by displaced organs underneath.
• External intercostal muscles relax, ribs fall.
• Volume of chest cavity decreases.
• Pressure in lungs increases, rises above atmospheric pressure.
• Air moves out of lungs.

Question 25

Explain the meanings of the terms tidal volume and vital capacity

Answer 25

Tidal volume- the volume of air in each breath-about 0.4dm^3

Vital capacity- the maximum volume of air that can be breathed in or out.

Question 26

Describe how a spirometer can be used to measure vital capacity, tidal volume, breathing rate and oxygen uptake

Answer 26

1. It has an oxygen-filled chamber with a movable lid.
2. The person breathes through a tube connected to the oxygen chamber.
3. As the person breathes in and out, the lid of the chamber moves up or down.
4. These movements are recorded by a pen, attached to the lid of the chamber. This writes on a rotating drum, creating a spirometer trace.
5. The soda lime in the tube (that the subject breathes into) absorbed carbon dioxide.

Question 27

analyse and interpret data from a spirometer…

Answer 27

…