Cell Biology

Question 1

What are eukaryotic cells?

Answer 1

have a cell membrane, cytoplasm and genetic material enclosed in a nucleus

Question 2

example of eukaryotic cells:

Answer 2

animal cells and plant cells

Question 3

What are prokaryotic cells?

Answer 3

They have cytoplasm and a cell membrane surrounded by a cell wall. The genetic material is not enclosed in a nucleus. It is a single DNA loop and there may be one or more small rings of DNA called plasmids.

Question 4

examples of prokaryotic cells:

Answer 4

bacterial cells

Question 5

what does the nucleus do?

Answer 5

this contains the genetic material (DNA) of the organism and controls the cell’s activities.

Question 6

what is cytoplasm?

Answer 6

the liquid that makes up most of the cell in which chemical reactions happen. This is mainly water.

Question 7

What is the cell membrane?

Answer 7

a flexible outer layer that surrounds the cell and controls which substances can pass into and out from it.

Question 8

What is mitochondria?

Answer 8

tiny parts of cells floating in the cytoplasm where energy is released from glucose from food. The mitochondria, found in the cell cytoplasm, are where most respiration happens.

Question 9

What is the cell wall?

Answer 9

a tough outer layer of the cell, which contains cellulose to provide strength and support to the plant.

Question 10

What is the vacuole?

Answer 10

a space inside the cytoplasm that contains a watery liquid called cell sap. It keeps the cell firm.

Question 11

What is the chloroplasts?

Answer 11

structures found in the cells of green parts of plants only (leaves and stems) which contain a green pigment called chlorophyll in which photosynthesis occurs.

Question 12

How are Nerve cells specialised?

Answer 12

They are thin, and can be more than 1 metre long. This means they can carry messages up and down the body over large distances.
Nerve cells have branched connections at each end. These join to other nerve cells, allowing them to pass messages around the body.
They have a fatty (myelin) sheath that surrounds them. The fatty sheath increases the speed at which the message can travel.

Question 13

How are muscle cells specialised?

Answer 13

Muscle cells are held together in bundles, which pull together to make muscles contract (get shorter and fatter).

Question 14

how are cardiac cells specialised?

Answer 14

Cardiac (heart) muscle cells are branched, and they join together to make a net. Cardiac muscle cells contract rhythmically, even outside the body. They never get tired.

Question 15

how are skeletal muscle cells specialised?

Answer 15

Skeletal muscle is joined to bones. Its cells contract to make bones move and joints bend.

Question 16

how are smooth muscle cells specialised?

Answer 16

Smooth muscle cells make up thin sheets of muscle, such as the stomach lining. They can also be arranged in bundles, or rings, like that in the anus.

Question 17

How are sperm cells specialised?

Answer 17

the head contains the nucleus with the DNA. The head contains enzymes so the sperm can penetrate the egg. It has mitochondria to release energy needed to swim and fertilise the egg. The tail enables the sperm to swim.

Question 18

How are root hair cells specialised?

Answer 18

They are long and thin so they can penetrate between soil particles and they have a large surface area for absorption of water.

Question 19

How are xylem cells specialised?

Answer 19

xylem are specialised cells called vessels.
Vessels: Lose their end walls so the xylem forms a continuous, hollow tube. Become strengthened by a chemical called lignin. The cells are no longer alive. Lignin gives strength and support to the plant. We call lignified cells wood. Transport in the xylem is a physical process. It does not require energy.

Question 20

how are phloem cells specialised?

Answer 20

Sieve tubes – specialised for transport and have no nuclei. Each sieve tube has a perforated end so its cytoplasm connects one cell to the next. Companion cells – transport of substances in the phloem requires energy. One or more companion cells attached to each sieve tube provide this energy. A sieve tube is completely dependent on its companion cell(s).

Question 21

what is cell division for?

Answer 21

cell division is mainly restricted to repair and
replacement. Cell division by mitosis is important in the growth and development of multicellular organisms

Question 22

what is cell differentiation?

Answer 22

As a cell differentiates it acquires different sub-cellular
structures to enable it to carry out a certain function. It has become a specialised cell.

Question 23

what is difference between an electron microscope and microscope?

Answer 23

An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.

Question 24

what is an equation for size of image (magnification)?

Answer 24

size of image = magnification x size of real object

Question 25

Describe the stages mitosis:

Answer 25

During the cell cycle the genetic material is doubled and then divided into two identical cells.
Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome. In mitosis one set of chromosomes is pulled to each end of the cell
and the nucleus divides. Finally the cytoplasm and cell membranes divide to form two
identical cells.

Question 26

what is a stem cell?

Answer 26

A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.

Question 27

How can human embryos be used for stem cells?

Answer 27

Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells.

Question 28

How can bone marrow be used for stem cells?

Answer 28

Stem cells from adult bone marrow can form many types of cells including blood cells.

Question 29

What are meristems?

Answer 29

Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant.

Question 30

What is therapeutic cloning?

Answer 30

In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patient’s body so they may be used for medical treatment.

Question 31

problems with using embryos:

Answer 31

The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections.

Question 32

Advantages of using stem cells in plants:

Answer 32

• Rare species can be cloned to protect from extinction.
• Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.

Question 33

What is diffusion?

Answer 33

Diffusion is the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.

Question 34

what are substances transported in and out of cells by diffusion?

Answer 34

oxygen and carbon dioxide in gas exchange, and of the waste
product urea from cells into the blood plasma for excretion in the
kidney.

Question 35

factors that affect the rate of diffusion?

Answer 35

• the difference in concentrations (concentration gradient)
• the temperature
• the surface area of the membrane.

Question 36

A single-celled organism has a relatively large surface area to volume ratio. What does this allow?

Answer 36

This allows sufficient transport of molecules into and
out of the cell to meet the needs of the organism

Question 37

In multicellular organisms, surfaces and organ systems are specialised for exchanging materials. what does this allow?

Answer 37

This is to allow sufficient
molecules to be transported into and out of cells for the organism’s
needs

Question 38

how can the effectiveness of an exchange surface be increased?

Answer 38

• having a large surface area
• a membrane that is thin, to provide a short diffusion path
• (in animals) having an efficient blood supply
• (in animals, for gaseous exchange) being ventilated.

Question 39

what is osmosis?

Answer 39

Osmosis is
the diffusion of water from a dilute solution to a concentrated
solution through a partially permeable membrane.

Question 40

What is active transport?

Answer 40

Active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). This requires energy from respiration. Active transport allows mineral ions to be absorbed into plant root
hairs from very dilute solutions in the soil. Plants require ions for healthy growth. It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration.