Cell structure (2)

Question 1

What are Eukaryotic cells?

Answer 1

They are cells that contain a nucleus. They are more complex than prokaryotic cells e.g. animal and plant cells.

Question 2

What are prokaryotic cells?

Answer 2

They are cells that don’t contain a nucleus. They are smaller and simpler than eukaryotic cells e.g. bacteria cells.

Question 3

What are organelles?

Answer 3

They are microscopic parts of cells, with each one having a specific function.

Question 4

What are the organelles found in an animal cell? (12)

Answer 4

• Cell surface membrane
• Rough endoplasmic reticulum
• Nucleolus
• Nucleus
• Smooth endoplasmic reticulum
• Lysosome
• Ribosome
• Nuclear envelope
• Golgi apparatus
• Cytoplasm/Cytosol
• Mitochondrion
• Centrioles

Question 5

What are the organelles found in a plant cell? (14)

Answer 5

• Cell surface membrane
• Chloroplast
• Rough endoplasmic reticulum
• Plasmodesmata
• Mitochondrion
• Golgi apparatus
• Vacuole
• Smooth endoplasmic reticulum
• Cytoplasm/Cytosol
• Nuclear envelope
• Nucleolus
• Nucleus
• Ribosome
• Cell wall

Question 6

What is the description and function of the Plasma cell surface membrane?

Answer 6

The membrane is found on the surface of animal cells and inside the cell wall in plant cells and prokaryotic organisms. It is primarily made up of lipids and proteins.
Its function is to regulate 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.

Question 7

What is the description and function of the Cell wall?

Answer 7

It is a rigid structure, made up of the carbohydrate cellulose, that surrounds plant cells.
Its function is to structurally support the plant cell.

Question 8

What is the description and function of the Nucleus?

Answer 8

It is a large organelle surrounded by the nuclear envelope (double membrane), which contains many pores. The nucleus contains chromatin (which is made from DNA and proteins) and a structure called the nucleolus.
Its function is to control the cell’s activities (by controlling the transcription of DNA). The pores allow substances to move between the nucleus and the cytoplasm. The Nucleolus makes ribosomes and RNA.

Question 9

What is the description and function of the Lysosome?

Answer 9

Lysosomes are round organelles surrounded by a membrane, with no clear internal structure. The membrane separates the internal digestive enzymes from the cytoplasm.
Its function is to carry digestive enzymes and use them to digest invading cells or to break down worn-out components of the cell.

Question 10

What is the description and function of the Ribosome?

Answer 10

Ribosomes are very small organelles that are either free-floating in the cytoplasm or attached to the RER. It is made up of proteins and RNA. It is not surrounded by a membrane.
Its function is the site of protein synthesis.

Question 11

What is the description and function of the Rough endoplasmic reticulum?

Answer 11

It is a system of membranes enclosing a fluid-filled space. The surface is covered with ribosomes.
The function of the REM is to fold and process proteins that have been made at the ribosomes.

Question 12

What is the description and function of the Smooth endoplasmic reticulum?

Answer 12

They are structurally similar to the RER but have no ribosomes.
Its function is to synthesize and process lipids.

Question 13

What is the description and function of the Vesicles?

Answer 13

Vesicles are a small fluid-filled sac in the cytoplasm, surrounded by a membrane.
The function of vesicles is to transport substances in and out of the cell (via the plasma membrane) and between organelles. Some are formed by the Golgi apparatus or the ER, while others are formed at the cell surface.

Question 14

What is the description and function of the Golgi apparatus?

Answer 14

The Golgi apparatus is made up of a group of fluid-filled, membrane-bound, flattened sacs. Vesicles are often seen at the edges of the sacs.
Its function is to process and package new lipids and proteins. It also makes lysosomes.

Question 15

What is the description and function of the Mitochondrion?

Answer 15

They are usually oval-shaped. They have a double membrane where the inner one is folded to form structures called cristae. Inside is the matrix, which contains enzymes involved in respiration.
Its function is that it’s the site of aerobic respiration where ATP is produced. They’re found in large numbers in cells that are very active and require a lot of energy.

Question 16

What is the description and function of the Chloroplast?

Answer 16

Chloroplasts are small, flattened structures found in plant cells. They are surrounded by a double membrane and also have membranes inside called thylakoid membranes. These membranes are stacked up in some parts of the organelle to form grana. Grana are linked together by lamellae (thin, flat pieces of the thylakoid membrane).
Its function is that it is the site of photosynthesis. Some occurs in the Grana and some in the Stroma (a thick fluid found in chloroplasts).

Question 17

What is the description and function of the Centrioles?

Answer 17

Centrioles are small, hollow cylinders made up of microtubules (tiny protein cylinders). They are found in animal cells, but only in some plant cells.
Its function is that it is involved in the separation of chromosomes during cell division.

Question 18

What is the description and function of the Cilia?

Answer 18

Cilia are small, hair-like structures found on the surface membrane of some animal cells. In cross-section, they have an outer ring of nine pairs of protein microtubules inside, with two microtubules in the middle.
Its function is that the microtubules allow the cilia to move. This helps move substances along the cell surface.

Question 19

What is the description and function of the Flagellum?

Answer 19

They are like cilia but longer. They stick out from the cell’s surface membrane and are surrounded by a plasma membrane. Inside there are cilia too, with two microtubules in the centre and nine pairs around the edge.
Its function is to contract to make the flagellum move. They are used like outward motors to propel cells forward.

Question 20

What are the steps of protein production in a cell? (Organelles)

Answer 20

1. Proteins are made at the ribosomes
2. The ribosomes on the RER make proteins that are excreted or attached to the cell membrane. The ribosomes that are free in the cytoplasm make proteins that remain in the cytoplasm.
3. New proteins created at the RER are folded and processed (e.g. sugars are added) in the RER.
4. Then they are transported from the ER to the Golgi apparatus via vesicles.
5. At the Golgi apparatus, the proteins can undergo further processing (e.g. more sugars are added or the chain is trimmed)
6. The proteins then enter more vesicles to be transported around the cell, or to the membrane to exit the cell.

Question 21

What is the cytoplasm and cytoskeleton?

Answer 21

The cytoplasm is the site of most chemical reactions in the cell. It is made up of a solution of chemicals with a network of protein threads running through it. These protein threads are called the cytoskeleton.
In eukaryotic cells, the protein threads are arranged as microfilaments (small solid strands) and microtubules (Tiny protein cylinders). The cytoskeleton is dynamic which allows it to respond to changes in the cell and carry out its functions.

Question 22

What are the main functions of the cytoskeleton? (4)

Answer 22

• The microtubules and microfilaments support the cell’s organelles, keeping them in position.
• They help to strengthen the cell and maintain its shape
• They are responsible for the movement of materials within the cells. (like chromosomes moving apart requires the contraction of microtubules in the spindle)
• The proteins of the cytoskeleton cause the cell to move. (Like the contracting protein filaments running through flagella and cilia)

Question 23

What are the sizes of Prokaryotes and Eukaryotes?

Answer 23

Prokaryotes are smaller- about 2 micrometers
Eukaryotes are larger- about 10-100 micrometers

Question 24

What are the differences between the DNA in Prokaryotes and Eukaryotes?

Answer 24

In Prokaryotes DNA is circular while in Eukaryotes DNA is linear.

Question 25

What is the difference between Prokaryotes and Eukaryotes in relation to the nucleus?

Answer 25

There is a nucleus in Eukaryotic cells while there is not one in Prokaryotic cells.

Question 26

What is the difference between Prokaryotes and Eukaryotes in relation to the cell wall?

Answer 26

In Prokaryotes there is a cell wall made up of a polysaccharide but it isn't cellulose or chitin. In Eukaryotes, there are cell walls in plants (cellulose), and cell walls in fungi (chitin), but none in animals.

Question 27

What is the difference between Prokaryotes and Eukaryotes in relation to organelles?

Answer 27

In Prokaryotes, there are few organelles and no membrane-bound ones like mitochondria. In Eukaryotes, there are many organelles and lots of membrane-bound ones like mitochondria.

Question 28

What is the difference between Prokaryotes and Eukaryotes in relation to flagella?

Answer 28

In Prokaryotes, flagella when present are made up of the protein flagellin arranged in a helix. In Eukaryotes, flagella when present are made up of microtubule proteins arranged in a 9 + 2 formation.

Question 29

What is the difference between Prokaryotes and Eukaryotes in relation to ribosomes?

Answer 29

In Prokaryotes, there are smaller ribosomes in comparison to Eukaryotes.

Question 30

What are some examples of a Prokaryote and Eukaryote?

Answer 30

Prokaryote - E. coli bacterium Eukaryote - Human liver cell

Question 31

What are some qualities of prokaryotic organisms?

Answer 31

- 1/10th the size of Eukaryotic organisms - Normal microscopes can't look at their internal structure so electron microscopes must be used. - The organelles usually found are: ribosomes, plasmids, cell wall, cell surface membrane, flagellum, and DNA

Question 32

What is magnification?

Answer 32

Magnification is how much bigger the image is than the specimen. It is calculated using the formula: magnification= image size/object size

Question 33

What is resolution?

Answer 33

Resolution is how detailed the image is. It's how well a microscope distinguishes between two points that are close together. If a microscope lens can't separate two objects then increasing the magnification won't help.

Question 34

What are the qualities of a light microscope?

Answer 34

- It uses light - They have a lower resolution than electron microscopes (0.2 micrometers) so they are usually used to look at whole cells or tissues. - The maximum magnification of a light microscope is about x1500

Question 35

What are the qualities of a Laser-scanning Confocal Microscope?

Answer 35

- It uses laser beams to scan a specimen, which is usually tagged with fluorescent dye. - The laser causes the dye to give off light (fluorescent). The light is then focused through a pinhole onto a detector. The detector is hooked up to a computer which produces an image. - The image can be 3D - The pinhole means that any out-of-focus light is blocked, so these microscopes give a much better image than regular light microscopes. - They can be used to look at objects at different depths in thick specimens.

Question 36

How do electron microscopes work?

Answer 36

They use electrons instead of light to form an image. They have a higher resolution than light microscopes so give more detailed images.

Question 37

What are the qualities of Transmission electron microscopes?

Answer 37

- Uses electromagnets to focus a beam of electrons, which is then transmitted through the specimen. - Denser parts of the specimen absorb more electrons, which makes them look darker in the final image produced. - TEMs are good because they provide high-resolution images (meaning you can look at organelles) but they can only be used on thin specimens.

Question 38

What are the qualities of Scanning electron microscopes?

Answer 38

- SEMs scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image. -The photos can be 3D but produce lower resolution pictures in comparison to TEMs

Question 39

What are the TEM's resolution and magnification values?

Answer 39

Magnification: can be more than x 1 000 000 Resolution: 0.0002 micrometers

Question 40

What are the SEM's resolution and magnification values?

Answer 40

Magnification: usually less than x 500 000 Resolution: 0.002 micrometers

Question 41

Why do we need to stain specimens before being viewed in a microscope?

Answer 41

In light microscopes and in TEMs, the beam of light/electrons passes through the object being viewed. An image is produced because some parts of the object absorb more light/electrons than other parts. Some parts appear white due to the object being transparent- so we use stains to get past this.

Question 42

How do you stain a sample for use in a light microscope?

Answer 42

- Light microscopes often need some form of dye like eosin and methyl blue. - The stain is taken up by some parts of the object more than others- the contrast helps the different parts show up. - Different stains are used to make different things show up (e.g. eosin for cytoplasm and methylene blue for DNA) - More than one stain can be used at once.

Question 43

How do you stain a sample for use in an electron microscope?

Answer 43

- Objects are dipped in a solution of heavy metals (like lead). The metal ions scatter the electrons, creating contrast as some parts of the object show up darker than others. - Electron microscope pictures are always colourless even when stained, but colour can be educated added to the picture after being acquired.

Question 44

How do you prepare a microscope slide?

Answer 44

1) for a light microscope you need to stick it on a slide first ( a wedge of glass either flat or with a small divot) 2) (wet mount) You need to put a drop of water onto your slide by using a pipette. Then use your tweezers to place your specimen on top. use a mount needle to lower the cover slip onto the specimen to avoid any air bubbles. 'then add a stain on the side of the cover slip and use a paper towel on the other size to draw the stain across. 3) (dry mount) You need a thin slice for the light to be able to get through. Use tweezers to place it in the middle of a slide and then add a cover slip on top.

Question 45

How do you use a light microscope?

Answer 45

1) Clip the slide you are looking at onto the stage 2) Start with the lowest objective lens and use the coarse adjustment knob to bring the stage up and the object is the most focused you can get 3) Then use the fine adjustment knob to further focus the object and you can achieve a clear image. 4) Then repeat on a greater objective lens if you need to see the object in greater magnification

Question 46

How do you find out the size of your specimen? (example)

Answer 46

1) Line up the eyepiece graticule and stage micrometer. 2) Each division on the stage micrometer is 0.1 mm long. 3) At this magnification ,1 division on the stage micrometer is the same as 4.5 divisions on the eyepiece graticule. 4) To work out the size of one division on the eyepiece graticule, you need to divide 0.1 by 4.5. This is 0.022 mm 5) So if you look at an object under the microscope at this magnification and its 20 eyepieces divisions long, you know it measures: 20 x 0.022 = 0.44 mm.

Question 47

What is an eyepiece graticule and a stage micrometer and how do they work together?

Answer 47

An eyepiece graticule is fitted onto the eyepiece of a microscope and is like a transparent ruler with numbers- but no units. A stage micrometer is placed on the stage and often is in the form of a slide. It has an accurate scale and units. They work together to work out the value of the divisions on the eyepiece graticule at a particular magnification. This means you can use it to measure the size of your specimen accurately.