B1 Cell Biology

What is a eukaryotic cell? (3)

Cells that make up plants and animals

They always have a nucleus

They have a cell membrane and cytoplasm

What are eukaryotic organisms?

Organisms which contain eukaryotic cells, like plants and animals

What is a prokaryotic cell? (2)

Cells that don’t have a nucleus - their DNA is stored in the cytoplasm

They are smaller than eukaryotic cells

What type of cell is a bacterial cell: prokayrotic or eukaryotic?

prokaryotic

What are prokaryotes? (2)

Usually single-celled organisms

They have no nuclei or organelles

What is smaller: an plant cell or a bacterial cell?

Bacterial cell.

What are the two forms of DNA found in bacterial cells? (2)

Circular strand of DNA which floats freely in the cytoplasm

Plasmids - small rings of DNA.

What is the role of the nucleus in a cell?

Contains DNA

What is the role of the ribosomes in a cell?

Make proteins

What is the role of the cytoplasm in a cell?

Where chemical reactions happen

What is the role of the mitochondria in a cell?

Where aerobic respiration occurs

What is the role of the vacuole in a cell?

Stores sap

What is the role of the chloroplasts in a cell?

Where photosynthesis happens

What is the role of the cell membrane?

Controls what enters and exits the cell

What is the role of the cell wall?

Strengthens the cell

What is the function of sperm cells?

Reproduction

What is the function of muscle cells?

Movement

What is the function of nerve cells?

Carrying messages quickly

What is the function of root hair cells?

Absorption of water and mineral ions

What is the function of phloem cells?

Transporting cell sap / food (translocation)

What is the function of xylem cells?

Transporting water (transpiration) and dissolved minerals

How are sperm cells specialised for reproduction? (3)

Long tail + streamlined head to swim to egg

Contain lots of mitochondria for respiration to generate energy for movement

Acrosome (layer round head) contains digestive enzymes to break down egg's membrane

How are muscle cells specialised for contraction?

Contain lots of mitochondria for respiration to generate energy for contraction

How are nerve cells specialised for rapid signalling? (3)

Long axon to carry information over long distances

Branches so that it can communicate with many other cells

Covered with a fatty sheath which increases the speed that the message moves at

How are root hair cells specialised for absorption?

Large surface area for absorption

How are xylem cells specialised for the transportation of water?

Dead cells form long, hollow tubes up which water can travel with little resistance

How are phloem cells adapted for the transportation of food substances

Living cells with few organelles form long tubes up which cell sap / food can travel with little resistance

What is cell differentiation? (2)

when a cell becomes specialised

This means it acquires different structures to enable it to carry out a certain function

When do animal cells usually differentiate?

at an early stage

When do plant cells usually differentiate?

anytime throughout their life

How do electron microscopes compare to light microscopes? (3)

More expensive

Higher resolution power

Higher magnification

What equation links size of image, size of object, and magnification?

magnification = size of image ÷ size of real object

How did electron microscopes affect biologists?

they allowed biologists to see and understand many more sub-cellular structures

What are chromosomes?

Coiled up lengths of DNA molecules.

How many chromosomes are in a human body cell?

23 pairs (46 in total)

Why do body cells normally have two copies of each chromosome?

One from the mother, one from the father.

What do genes control?

The development of different characteristics.

What is the cell cycle?

The process in which a cell grows, then divides to form two genetically identical cells

What is the importance of the cell cycle?

repair and replacment of cells, and the growth and development of organisms

What are the three phases of the cell cycle? (3)

1) Growth

2) Mitosis

3) Division

What happens in the growth phase of the cell cycle?

the DNA replicates to form two copies of each chromosome, and the number of sub-cellular structures (such as ribosomes and mitochondria) increases

What happens in the mitosis phase of the cell cycle?

one set of chromosomes is pulled to each end of the cell and the nucleus divides

What happens in the cell division phase of the cell cycle?

the cytoplasm and cell membranes divide to form two identical cells

What is a stem cell?

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

What are embryonic stem cells?

Unspecialised cells in embryos which can develop into any type of cell

What are adult/mature stem cells?

Stem cells found in adults.They cannot differentiate into any type of cell; for example, bone marrow stem cells can become red blood cells but not gametes

What is the main function of mature stem cells in the body?

Repairing and replacing cells.

What are meristem cells?

unspecialised cells that can differentiate into any type of plant cell, throughout the life of the plant

Where in plants is meristem tissue found?

The tips of shoots and in the roots.

What conditions can be treated using stem cells?

diabetes and paralysis, among others

What is therapeutic cloning?

A process which produces an embryo with the same genes as the patient. This means that the stem cells produced by the embryo are not rejected by the patient's body during medical treatment.

Why are some people against stem cell research?

They have ethical or religious objections

What are the pros of using stem cells to cure disease?

1) Improves lifestyles of people with some diseases

2) Can reduce/remove side effects compared to other treatments

What are the cons of using stem cells to cure disease?

1) Can be very expensive.

2) Not a fully developed technology; long term effects unknown.

3) Can only work in specific cases

How can we use stem cells from meristems?

Cloning plants quickly and economically, so that we can:

1) Protect rare species from extinction.

2) Clone plants with desired features for farmers, e.g. disease resistance.

What is diffusion?

net movement of particles from an area of higher concentration to an area of lower concentration

What substances move in and out of human cells by diffusion?

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

What factors increase the rate of diffusion across a membrane?

- Surface area of the membrane

- Temperature

- Higher concentration gradient

How are surfaces in organisms adapted for efficient exchange of substances?

1) Thin membranes

2) Large surface area

3) lots of blood vessels in animals

4) good ventilation (lots of gases moving past)

What is the inside of the small intestine covered in?

Villi (which increase surface area)

How is the structure of villi related to their function?

1) They increase the surface area of the small intestine.

2) They are thin to reduce the distance across which diffusion occurs

3) They have a good blood supply for the uptake of substances.

How is the underneath of a leaf adapted for diffusion of gases?

1) Covered in stomata

2) large surface area

3) Air spaces between cells inside leaf increase ventilation

What is the gas exchange surface in fish?

The gills.

How is the structure of gills adapted for gas exchange?

1) large surface area for gas exchange

2) thin to reduce the distance across which diffusion occurs

3) good blood supply

4) A large concentration gradient is maintained between the water and blood, so rate of diffusion into blood is maximised

What is osmosis?

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

What is active transport?

when substances move from a more dilute solution to a more concentrated solution (against a concentration gradient). This requires energy from respiration

What are examples of active transport?

1) mineral ions are absorbed into plant root hairs from very dilute solutions in the soil

2) sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration