Cells

Question 1

What about cells suggests that all organisms come from the same ancestors?

Answer 1

They are all made up of cells which have the same basic features and organelles.

Question 2

What are organelles?

Answer 2

Part of a cell that have a specific functiob.

Question 3

What are eukaryotic cells and what are the examples?

Answer 3

More complicated cells with more organelle and a membrane bound nucleus. The examples are animal cells, plant cells, algal cells and fungal cells.

Question 4

What are the 11 organelles in animal cells?

Answer 4

Nucleus, ribosomes, lysosomes, mitochondria, Golgi apparatus, rough endoplasmic reticulum, smooth endoplasmic reticulum, cell membrane, cytoplasm, nuclear envelope, nucleolus.

Question 5

What are the 3 additional organelles only found in plant cells?

Answer 5

Chloroplast, cell wall and a vacuole.

Question 6

Describe the nucleus (parts and what they do).

Answer 6

Nuclear envelope - double membrane around the nucleus. Outer one is like the RER (has ribosomes on it) and it controls the entry and exit of material into the nucleus.
Nuclear pores - allow the passage of large molecules such has messenger RNA out of the nucleus.
Nucleoplasm - granular, jelly-like material that makes up the bulk of the nucleus.
Nucleolus - small spherical region found in the nucleoplasm. It creates ribosomes by manufacturing ribosomal RNA.

Question 7

What are the functions of the nucleus?

Answer 7

Acts as the control center of the cell and controls the activities.
Holds the cell’s hereditary/genetic material through DNA and chromosomes.
Makes ribosomes and ribosomal RNA.

Question 8

Describe mitochondria (parts and what they do).

Answer 8

Double membrane - surrounds the organelle and controls the entry and exit of material. The inner membrane contains folds (cristae).
Cristae - extensions in the inner membrane which can sometimes extend across the whole mitochondrion. These provide a large surface area for proteins and enzymes involved in respiration to attach to.
Matrix - makes up the remainder (inside) of the mitochondrion. It holds proteins, lipids and also DNA and ribosomes to help the mitochondria make its own proteins.

Question 9

What is the function of the mitochondria?

Answer 9

The site of aerobic respiration.
Responsible for the production of ATP from respiratory substances such as glucose. Therefore, cells which require more energy such as epithelial or muscle cells have a lot of mitochondria and bigger mitochondria. Furthermore, cells which undergo active transport require a lot of ATP, and therefore mitochondrion.

Question 10

Describe chloroplasts (parts and what they do).

Answer 10

The chloroplast envelope - double membrane that surrounds the organelle. It is highly selective of what it allows through.
Grana - stacks of up to a 100 disc-like structures called the thylakoids. Between these is a pigment called chlorophyll. Some thylakoids have extensions called lamellae which connect to other thylakoids in adjacent grana. The grana is where the first stage of photosynthesis (light absorption) happens.
The stoma - a fluid filled matrix where the second stage of photosynthesis (synthesis of sugar) occurs. It is filled with other structures, such as starch grains.

Question 11

How has the chloroplast adapted for its function?

Answer 11

The grana membranes have a high surface area for the attachment of chlorophyll, electron carriers and enzymes for the first stage of photosynthesis to occur.
The fluids in the stroma contain all the enzymes required to make sugars for the second stage of photosynthesis.
Chloroplasts contain both DNA and ribosomes so they can quickly manufacture proteins needed for photosynthesis.

Question 12

What is the rough endoplasmic reticulum?

Answer 12

A system of sheet-like membranes that spread out in the cytoplasm. There are ribosomes found on the outer surface of its membrane, therefore is continuous with the outer membrane of the nucleus. The membranes enclose a network of flattened sacs called cisternae.

Question 13

What is the function of the rough endoplasmic reticulum?

Answer 13

Folds and processes proteins made at the ribosomes.
Provides a pathway for the transport of materials, especially proteins, throughout the cell.

Question 14

What is the smooth endoplasmic reticulum?

Answer 14

A system of sheet-like membranes that spread out in the cytoplasm, without ribosomes on the surface. They have flattened sacs called cisternae.

Question 15

What is the function of the smooth endoplasmic reticulum?

Answer 15

Synthesizes, stores and transports lipids.
Synthesizes, stores and transports carbohydrates.

Therefore, is synthesizes, stores and transports some substances required by the cell.

Question 16

What is the Golgi apparatus?

Answer 16

A stack of small sacs called cisternae. They have small vesicles at the edges of their sacs.

Question 17

What is the function of the Golgi apparatus?

Answer 17

It receives proteins from the rough endoplasmic reticulum and modifies them (often adding carbohydrates to them) and labels them to be sent to the right place.
It receives lipids from the endoplasmic reticulum and modifies and stores them.
The proteins and lipids are transported in the Golgi vesicles which takes them to the cell surface, where it fuses and releases the components.
It makes lysosomes.
Produces secretory enzymes.

Question 18

What are lysosomes?

Answer 18

A round organelle surrounded by a membrane. It is made when Golgi vesicles contain enzymes such as protease and lipase.
Contain lysozymes which are a digestive enzyme which hydrolyze the wall of certain bacteria.
These cells are kept in the lysosome away from the cytoplasm but can be released when needed to digest invading cells or worn out components of the cell.

Question 19

What is the function of the lysosomes?

Answer 19

Hydrolyze the materials ingested by phagocytic cells such as white blood cells which ingest bacteria.
Release enzymes outside the cell to destroy any bacteria around the cell.
Digest worn out organelles so the material they are made up from can be reused.
Completely break down cells after they have died.

Question 20

What are ribosomes?

Answer 20

Small cytoplasmic granules found in all cells. There are two types depending on the type of cell they are in:
80s - found in eukaryotic cells and is much bigger.
70s - found in prokaryotic cells, mitochondria and chloroplasts. These are much smaller in size.

Ribosomes have two subunits - one big and one small. They both contain ribosomal RNA and proteins.
Although ribosomes are small, there are so many of them that they make up 25% of the cell’s dry mass.

Question 21

What is the function of ribosomes?

Answer 21

They are the site of protein synthesis.

Question 22

What is the cell wall?

Answer 22

Consists of polysaccharides (such as cellulose) and microfibrils, which are embedded in a matrix. Cellulose microfibrils have a lot of strength and so contribute to the strength of the cell wall.
There is a thin layer called the middle lamella which cements the two adjacent cell wall layers together.

Cell walls in plants are made up of cellulose.
Cell walls in algae are made up of either cellulose of glycoproteins.
Cell walls of fungal cells contain neither but are made of chitin.

Question 23

What is the function of the cell wall?

Answer 23

Provides mechanical strength to help prevent the cell from bursting due to pressure from osmotic intake/entry of water.
Gives mechanic strength to the plant overall.
Contributes to the movement of water through the plant.

Question 24

What is the vacuole?

Answer 24

A fluid filled sac surrounded by a membrane.
The single membrane around it is called the tonoplast.
It contains a solution of sugars, salts, amino acids and wastes.

Question 25

What is the function of the vacuole?

Answer 25

Support plants by making them turgid. Sugars and amino acids act as a store. Pigment may color petals to attract pollinating insects.

Question 26

How is cell ultrastructure related to its function?

Answer 26

As each organelle has a specific function, it is possible to deduce what type of cell it is depending on how much and how big each of its organelles are. For example, a cell which required a lot of energy has a lot of mitochondria, or mitochondria with a lot of cristae for ATP production.

Question 27

What is cell specialization?

Answer 27

Each cell in the body has adapted to better suit its function. The first cells in an embryo are identical, however over time they will all evolve to have either more or less organelles for this functions. However, they all have the same genes as they all developed mitotically, but some of these genes are switches either on or off depending if they are needed.

Question 28

What is a tissue?

Answer 28

A group of specialized cells that perform a particular function.

Question 29

What are two examples of tissues?

Answer 29

Epithelial tissues- these line the surface of organs and often have a protective or secretory function. Xylem tissues - found in plants and is used to help transport water and provide mechanical support.

Question 30

What is an organ?

Answer 30

Several different tissues with different functions grouped together to provide one major main function.

Question 31

What are the tissues that make up the stomach?

Answer 31

Muscle tissue - churns the food. Epithelial tissue - lines the stomach and provides protection and produces secretions. Connective tissue - connects all the tissues together.

Question 32

What tissues make up a leaf?

Answer 32

Palisade mesophyll tissue Spongy mesophyll tissue Epidermis tissue Xylem tissue Phloem tissue

Question 33

Why are blood capillaries not organs but veins and arteries are?

Answer 33

Although they all have the same function which is transporting blood, blood capillaries are made out of one tissue whereas veins and arteries are made out of several different tissues.

Question 34

What is an organ system and what are three main examples in the human body?

Answer 34

Different organs with different functions which work together to create a single unit. Three main examples: Digestive system - digest and processes food. Respiratory system - to breathe and exchange gas. Circulatory system - pumps, transports and circulates blood around the body.

Question 35

What is a prokaryotic cell?

Answer 35

Prokaryotes are single-celled organisms (such as bacteria) that do not have membrane bound organelles (such as nucleus). They are much smaller and less complex than eukaryotic cells. They occur in every habitat in the world - they are versatile and adaptable.

Question 36

What is the cellular structure of a prokaryotic cell?

Answer 36

Cell wall - made of murein (a glycoprotein - protein with carbohydrate). It helps support cell and prevent it changing shape. Capsule - slime around the cell to protect it from attack by cells in immune system. Cell membrane - made of lipids and proteins controls entry and exit of material. Cytoplasm - makes bulk and contains ribosomes (70s ribosomes so are smaller). Circular strand of DNA - the genetic material of the cell in one long strand. DNA is not linked with protein in bacteria. Plasmids - small loop of DNA, they can replicate on their own and they help with survival in extreme conditions such as antibiotic resistance. Flagellum - a tail that rotates to help the prokaryote move. Not all prokaryotes have a flagellum, some have several.

Question 37

Describe the process of binary fission.

Answer 37

1. The main circular DNA replicated once, the plasmids replicate several times. 2. The cell gets bigger, the circular DNA moves to either sides of the cell. 3. The cytoplasm begins to divide, and the cell wall begins to form. 4. The cytoplasm divides into two daughter cells. Each cell has one circular DNA loop but a random number of copies of the plasmids.

Question 38

What are viruses? Give some examples and how they exist.

Answer 38

Viruses are not cells. They are just a nucleic acid (which is their DNA) which is surrounded by a protein called a capsid. They are not alive so they invade and reproduce inside other cells (called host cells) in organisms. Some examples are HIV, influenza and rhinoviruses.

Question 39

Describe the structure of viruses.

Answer 39

Viruses do not have a cell membrane, cytoplasm or ribosomes. They just have a capsid (some have a lipid coating too) with attachment proteins sticking out of it so it can attach to a host cell.

Question 40

Describe viral replication.

Answer 40

Viruses do not undergo cell division as they are not alive. Instead, they attach to a host cell through they attachment proteins. The attachment proteins attach to the complementary receptor proteins on the cell surface of the host cell. Next, they inject their nucleic acid and therefore its genetic material into the host cell, which uses its components as instructions to replicate the viral particles.

Question 41

Why can viruses only infect certain cells?

Answer 41

The attachment proteins on their surface must be complementary to the receptor proteins on the host cell. Therefore, different viruses need different receptor proteins and will therefore infect different cells. Some an only infect one type of cell, while others can infect several.

Question 42

What is magnification and what is the equation?

Answer 42

How much bigger an image is than the specimen being looked at. The material under the microscope is known as the object. The equation is: Magnification = size of image / size of object

Question 43

Name the measurements used in magnification.

Answer 43

1 millimeter (mm) = 1000 micrometers (um) 1 micrometer (um) = 1000 nanometers (nm)

Question 44

What is the resolution?

Answer 44

How detailed an image is and how able a microscope is to distinguish between two points close together. The resolving power depends on the wavelength (shorter, higher resolution) and type of radiation. Once the resolution limit is reached, increasing the magnification will not help. The image will get bigger, but just be blurry.

Question 45

What is cell fractionation?

Answer 45

The process of breaking up a cell into its separate organelles so they can be isolated and even studied.

Question 46

Before cell fractionation, the tissue is placed in a solution. What are three things that the solution must be?

Answer 46

1. Cold - prevents enzyme activity which could break down organelles. 2. Buffer - prevents pH fluctuation which could lead to denaturing the enzymes or changing their shape. 3. Same water potential - the organelles do not shrink or burst due to osmotic water gain/loss.

Question 47

What are the four steps of cell fractionation?

Answer 47

1. Before beginning, place the tissue in a cold, isotonic solution. 2. Homogenization. 3. Filtration 4. Ultracentrifugation.

Question 48

What is the homogenization stage of cell fractionation?

Answer 48

The process of actually breaking up the cell. This can be done in several ways, for example vibrating the cell, or placing it in a blender called a homogenizer. This breaks the plasma membrane and releases the organelles into the solution, which is called the homogenate.

Question 49

What is the filtration stage of cell fractionation?

Answer 49

The homogenate is filtered through a gauze to get rid of any cell debris or tissue such as connective tissue. The organelles are much smaller than debris, so they pass through the filtration.

Question 50

What is the ultracentrifugation stage of cell fractionation?

Answer 50

After filtration, there is a homogenate solution with a lot of different organelles which need to be separated. 1. The solution is poured into a tube and placed in a centrifuge (a machine that spins around). 2. The tube is spun on low speed and the heavier organelles, such as nuclei, get pushed into the bottom and they form a thick sediment called a pellet. 3. The rest of the organelles stay in the solution above - the supernatant. 4. The supernatant is drained off and placed into a different tube, then spun again but at a higher speed. Again, the heavier organelles are flung onto the bottom and create a pellet. 5. This is repeated, each time with a faster spinning speed, until all the organelles are separated.

Question 51

What is an optical microscope?

Answer 51

These use light to form an image. They have an optimum resolution of 0.2 um, meaning they cannot see smaller organelles such as lysosomes, endoplasmic reticulum and ribosomes. Larger organelles such as nucleus and mitochondria can be seen but not in huge detail. They have a low resolution due to light having a long wavelength.

Question 52

What is an electron microscope and two advantages?

Answer 52

A microscope which uses a beam of electrons rather than a beam of light. A vacuum chamber must be near an electron microscope so the electrons do not get absorbed or deflected by molecules in the air. Two advantages are: 1. Electrons have a very short wavelength so the resolution is much higher. 2. Electrons have a negative charge so they can be focused using electromagnets.

Question 53

What are the two types of electron microscope?

Answer 53

1. Transmission electron microscope. 2. The scanning electron microscope.

Question 54

What is the transmission electron microscope?

Answer 54

A beam of electrons that are produced by an electron gun focused onto the specimen by a condenser electromagnet, which passes through a thin section of the specimen. Part of the specimen absorb the electrons so absorb dark, while other parts let the electrons pass through so appear light. An image is produced onto a screen, which can be photographed to create a photomicrograph.

Question 55

Why can the optimum resolving power not always be reached in a transmission electron microscope?

Answer 55

Due to difficulty preparing and setting up the specimen. Also, it would require a higher beam energy which could destroy the specimen.

Question 56

What are some limitations of a transmission electron microscope?

Answer 56

- Must be in a vacuum so cannot be used to look at living things. - Can only be used on thin specimens and produced flat 2D images. - A complex staining process is required. - Image may contain artefacts which are not a part of the specimen.

Question 57

How can a 3D image be formed from a transmission electron microscope?

Answer 57

Taking 2D photomicrographs from different parts and sections then building them up.

Question 58

What is the scanning electron microscope?

Answer 58

Directs a beam of electrons from the top, which is passed up and back across the specimen in a pattern. The electrons then are scattered by the specimen in a specific pattern depending on the contours on the specimen's surface. Therefore, we can build a 3D image using this pattern.

Question 59

What are some limitations of the scanning electron microscope?

Answer 59

- Must be in a vacuum so cannot be used to look at living things. - A complex staining process is required. - Image may contain artefacts.

Question 60

Compare the transmission electron microscope and the scanning electron microscope.

Answer 60

Transmission microscope has high resolution, scanning microscope has a lower resolution. Transmission microscope must have a thin specimen, scanning microscope can have a thick one.

Question 61

Describe the process of preparing a microscope slide.

Answer 61

1. Using a pipette, add a drop of water onto a slide. 2. Use tweezers to place a thin layer of the tissue onto the water. 3. Add a suitable stain to highlight the organelles. 4. Place a cover slip upright next to it and slowly lower, to prevent any air bubbled forming. The cover slip is to protect it.

Question 62

What are two examples of stains used in microscopy?

Answer 62

Iodine is used to make starch grains show up in plant cells. Eosin is used to make the cytoplasm show up.

Question 63

What are artefacts?

Answer 63

Things that can be seen when looking down a microscope but are not parts of the specimen. This could be dust, air bubbles, fingerprints or anything wrong done during preparing the slide such as from squashing or staining the sample. Usually common in electron microscopes as the sample needs a lot of preparation.

Question 64

How do scientists identify artefacts?

Answer 64

Prepare the sample in many different ways and checking. If something can only be seen using one method of preparation, it is most likely an artefact.

Question 65

What is an eyepiece graticule?

Answer 65

An eye disc that is placed on the eyepiece of a microscope, with a scale on the glass. This can be used to measure the size of an actual object in a light microscope. The scale is usually 10mm long and divided into 100 subdivisions, and it is visible when looking down the eyepiece.

Question 66

Why does an eyepiece graticule have to be calibrated?

Answer 66

The scale cannot be used to measure the object as each objective lens will magnify to a different degree. The graticule must be calibrated to a specific lens, which can then be saved for the future.

Question 67

How do you calibrate an eyepiece graticule?

Answer 67

A stage micrometer is used. This slide has a scale etched onto it and when these two line up, it is possible to calculate the length of the divisions on the eye piece graticule. It is possible to find the scale for a different objective lens by dividing the difference in magnification.

Question 68

What are the two types of cell division?

Answer 68

Mitosis - produces two daughter cells that have the same number of chromosomes as each parent cell. Meiosis - produced four daughter cells, each with half the number of chromosomes as the parent cells.

Question 69

What is mitosis?

Answer 69

Mitosis is when a cell divides and results with two identical daughter cells with the exact DNA as the parent cell, unless in the rate occasion of a mutation. It is used in organisms for growth and for repairing damaged tissues.

Question 70

What is interphase?

Answer 70

Interphase is a stage that occurs before mitosis, preparing the cell to divide by replicating its DNA and its genetic material. The organelles are also replicated and ATP production is increased (energy needed for division).

Question 71

What are the four stages of mitosis?

Answer 71

1. Prophase 2. Metaphase 3. Anaphase 4. Telophase/Cytokinesis

Question 72

Explain the first stage of mitosis.

Answer 72

Prophase: The chromosomes shorten and thicken. Tiny bits of protein, called centrioles, go to either side of the cell and develop into spindle fibers, which span the cell (animal cells) from pole to pole. These are collectively called spindle apparatus. Plant cells do not have centrioles, but they have spindles. The nucleolus disappears and the nucleus envelope begins to break down, meaning the chromosomes lie freely in the cytoplasm.

Question 73

Explain the second stage of mitosis.

Answer 73

Metaphase: The chromosomes (which are each made of two chromatids attached by the centromere) line up in the middle of the cell and attach to the spindles by their centromeres.

Question 74

Explain the third stage of mitosis.

Answer 74

Anaphase: The centromere divides into two and the spindle fibers pull the two chromatids apart. The chromatids are pulled rapidly to the opposite side of the cell - centromere first (forming a v shape). This energy is provided by the mitochondria.

Question 75

What happens if a chemical is added to a cell that affects the spindle fibers?

Answer 75

The chromatids would stay in the middle and would not be split apart, as the spindles cannot pull it apart properly.

Question 76

Explain the fourth stage of mitosis.

Answer 76

Telophase/Cytokinesis: Chromatids reach polar sides with the spindles. They uncoil and become long again. They are now called chromosomes again. A nuclear envelope forms around each group of chromosomes, forming a nucleus. The cytoplasm begins to divide (cytokinesis) and forms two daughter cells with identical genetics to each other and to the parent cell. Mitosis is finished and each of the cells undergoes interphase again, ready to divide.

Question 77

What are the three stages of the cell cycle?

Answer 77

Interphase - occupies most of the cell cycle time and is sometimes known as resting phase as no divisions occur. Nuclear division - when nucleus divides into two (mitosis) or four (meiosis). Cytokinesis - when the cytoplasm divides to make two new cells (mitosis) or four new cells (meiosis).

Question 78

How does cancer occur?

Answer 78

Mitosis and the cell cycle are controlled by genes, including instructing the cells when to stop dividing once they have enough. However, if there is a mutation in the genes that control cell division, the cells could keep dividing and grow out of control, eventually forming a tumor. Cancer is a tumor that invades its surroundings.

Question 79

What are the two types of tumors?

Answer 79

Benign - non cancerous. It grows slowly and is not life threatening. Malignant - cancerous. It grows rapidly, is compact and can be life threatening.

Question 80

How is cancer treated?

Answer 80

Cancer treatment involves controlling the rate of cell division by disrupting the cell cycle, which kills the tumor cells. The treatments cannot distinguish the difference between the tumor cells and the normal cells, therefore can kill normal body cells dividing. However, tumor cells divide much more frequently than normal cells therefore are more likely to be killed. This can happen in two ways: 1. Prevent DNA replication. 2. Stop metaphase by interfering with the spindle formation.

Question 81

Explain the investigating mitosis practical

Answer 81

1. Add hydrochloric acid to a test tube and place into a boiling bath. 2. Use a scalpel to cut off the tip from the growing root - this is where growth occurs. 3. Add into the test tube and incubate for 5 minutes. 4. Use tweezers to remove tip from the acid and use a pipette to rinse with water, then leave to dry on a paper towel. 5. Place the root tip on a microscope slide and cut 2mm off the end. 6. Use a mounted needle to break the end and spread the cells out. 7. Add a few drops of stain. 8. Place a cover slip on top and some filter paper. Squish it down to spread out the cells and make it thinner for light to pass through. Do not move sideways as that could damage the chromosomes. 9. Look at it under an optical microscope.

Question 82

Explain the process of using an optical microscope.

Answer 82

1. Clip the prepared slide onto the stage. 2. Set it to the lowest objective lens with the lowest magnification. 3. Use the coarse adjustment knob to move the stage up. 4. Look down the eyepiece and move the coarse adjustment knob until it is roughly focused. 5. Adjust the fine adjustment knob to focus it more. 6. Increase the objective lens if a larger magnification is required.

Question 83

What are four things needed if you are asked to draw the cells undergoing mitosis?

Answer 83

1. The relative sizes in the object are accurate. 2. Write down the magnification of the specimen. 3. Label the drawing. 4. Add a title.

Question 84

What is the mitotic index?

Answer 84

This is the proportion of cells in a tissue undergoing mitosis. mitotic index = num of cells with visible chromosomes/ total cells in tissue For example, a plant root tissue is always growing so there would be a high mitotic index. In other tissues, a high mitotic index could mean there is a tissue repair taking place or there is cancerous growth in a tissue.