Cell Biology

What are eukaryotic cells?

Contain a nucleus and other organelles that are bound by membranes.

What are prokaryotic cells?

Cells that do not have a nucleus or other membrane-bound organelles.

How is a prokaryote different to a eukaryote?

They are usually unicellular, much smaller and have a cell wall made of peptidoglycan rather than cellulose.

Where is genetic material stored in prokaryotes?

Prokaryotes, like bacteria, store genetic material in plasmids (rings of DNA) or a singular large loop of DNA.

What are the average sizes of a prokaryotic cell and eukaryotic cell?

Prokaryotic - 1 to 5μm

Eukaryotic - 100 μm

What are all the sub-cellular structures?

The nucleus, cytoplasm, cell membrane, mitochondria, ribosomes, and in plants, chloroplasts, a cell wall and a (permanent) vacuole. In prokaryotes there can be pili, flagella, plasmids and slime capsules.

What is the function of the nucleus?

The nucleus contains the cell's genetic material (DNA) and controls the cell's activities.

What is the function of the cytoplasm?

The cytoplasm is a jelly like substance where most of the chemical reactions take place in the cell.

What is the function of the mitochondria?

The mitochondria are the site of aerobic respiration, where energy is released in the cell.

What is the function of the ribosomes?

Ribosomes are the site of protein synthesis.

What is the function of the cell membrane?

The cell membrane controls the movement of substances into and out of the cell.

What are the function of the chloroplasts?

The chloroplasts are the site of photosynthesis, containing a green pigment called chlorophyll that absorbs light for energy for photosynthesis

What is the function of the cell wall?

The cell wall is made of cellulose and provides support and strength to the cell.

What is the function of the (permanent) vacuole?

The permanent vacuole contains cell sap and helps to maintain the cell's shape and support by keeping the cell swollen and rigid.

What is the function of the pili?

Pili allow bacteria to attach to surfaces and allow them to exchange genetic material through plasmids.

What is the function of the slime capsule?

The slime capsule provides protection for the bacterium and allows it to attach to surfaces.

What is a stem cell?

A stem cells is a cell that has not undergone differentiation, so it has the ability to specialise into any type of body cell.

What is the name of the process where a stem cell becomes specialised?

Differentiation (not specialisation)

What are the types of specialised animal cells?

Nerve cell, sperm cell and muscle cell.

What are the types of specialised plant cells?

Xylem cells, Phloem cells and root hair cells

What are the adaptations of a sperm cell?

- Streamlined head and long tail to aid swimming.

- Many mitochondria (where respiration happens) which supply the energy to allow the cell to move.

- The head (acrosome) has digestive enzymes which break down the outer layers of membrane of the egg cell.

What are the adaptations of a nerve cell?

- Dendrites, which are branched endings that increase surface area to make more connections.

- A myelin sheath, which insulates the axon to increase the transmission speed of the electrical impulses.

- Synapses, which are junctions, allowing the impulses to pass to other nerve cells.

- A long axon, which allows impulses to be carried large distances.

- Many mitochondria make neurotransmitters which are transmit the impulses to other cells.

What are the adaptations of a muscle cell?

- contains protein fibres (myosin and actin), w hich can contract to make the cells shorter

- contains lots of mitochondria to release energy from respiration, allowing muscles to contract

- They store a chemical called glycogen, which is a storage form of glucose, for respiration

What are the adaptations of a xylem cell?

- When they are formed a chemical called lignin kills the cells, giving them a large lumen

- The cells are empty so it forms a continuous tube for water and mineral to flow

- The walls are thickened with lignin so they are much stronger

What are the adaptations of a phloem cell?

- Made of living cells which are supported by companion cells.

- Cells are joined end-to-end and contain holes in the end cell walls (sieve plates) forming tubes which allow sugars and amino acids to flow easily through (by translocation).

- Phloem cells also have very few sub cellular structures, relying on companion cells.

What are the functions of a root hair cell?

- Plenty of mitochondria for active transport.

- Thinner cell wall for a shorter diffusion/ exchange path.

- Larger permanent vacuole speeds up osmosis by a steeper concentration gradient.

What are the 2 ways cells can divide?

Meiosis (for gametes only) and mitosis

What does the nucleus contain?

The nucleus of a cell contains chromosomes made of DNA molecules.

What is a gene?

A section of DNA which codes for a protein.

What is a haploid cell?

There is only 1 pair of chromosomes, so there are only 23. These are gametes.

What is a diploid cell?

The cell has 2 pairs of 23 chromosomes, so 46 chromosomes. These are regular body cells as they are paired.

What are the stages of the cell cycle?

There are 3 stages:

- Interphase (Replication of DNA and increased number of organelles as well as cell growth).

- Mitosis (the division of the nucleus).

- Cytokinesis.

What is the interphase in the cell cycle?

Cell growth and the replication of DNA as well as increased formation of organelles.

What is the mitosis in the cell cycle?

Mitosis in the cell cycle is made up of prophase, metaphase, anaphase and telophase.

What happens in prophase in mitosis?

The chromosomes condense, making them more visible. The nucleus membrane disappears.

What happens in metaphase in mitosis?

In metaphase, chromosomes line in the equator (middle) of the cell.

What happens in anaphase in mitosis?

Spindle fibres pull the sister chromatids apart, moving one chromatid from each chromosome to each and opposite poles of the cell.

What happens in telophase in mitosis?

New membranes form around the chromosomes at each end of the cell, forming 2 nuclei that are genetically identical.

What is cytokinesis in the cell cycle?

Cytokinesis is the division of the cytoplasm, completing the cell cycle and the cell membrane forms around each of the daughter cells.

What does mitosis produce?

2 genetically identical diploid daughter cells

Why is mitosis useful?`

- Produces genetically identical cells

- Helps produce more cells so the organism can grow

- More cells also can be used for repair

What is a stem cell?

A cell that can differentiate and become any type of human cell`

What are some of the types of stem cells?`

Embryonic - differentiates into every type of cell, found i

Meristem tissue - differentiates into every type of plant cell, found in the tips of growing shoots and roots

Adult stem cells - found in bone marrow and can differentiate into any blood cell

What are some advantages of embryonic stem cells?

- Can treat a wide range of diseases as can form any specialised cell

- may be possible to grow whole replacement organs

- sometimes no donor needed as they are obtained from spare embryos from fertility clinics

What are some disadvantages of embryonic stem cells?

- Ethical issues, as the embryos have potential for life and are being destroyed

- Rejection risks, as the patients immune system may recognise the stem cells as a threat and attack them, so they have to take immunosupressent drugs

- They divide rapidly, however this can also cause the issue of tumors

What are advantages of adult stem cells?

- Permission can be given to collect stem cells and they are safe.

- There isnt a risk of rejection as its the patients own cells

What are disadvantages of adult stem cells?

- Doesnt divide as rapidly

- Only differentiates into a limited range of cells

What is therapeutic cloning?

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.

How does therapeutic cloning work?

An egg cell has its nucleus removed, and it is replaced with the nucleus of the patient's cell. The egg cell is then stimulated to divide by mitosis, as if it was a zygote. This starts to form an embryo, and, at the 8 cell stage, the stem cells are taken. The cells are then grown in a container with warm nutrients, and treated to develop properly into the cell type required.

What are advantages of therapeutic cloning in animals and plants?

- We can produce genetically identical cells so there is a lower chance of rejection

- Save rare species by cloning them

- We can maintain useful traits in plants e.g temperature resistance

What is diffusion?

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

What is osmosis?

The net movement of water from an dilute solution (more water) to a concentrated solution (less water)

What is active transport?

The net movement of molecules from a more dilute (more water less molecules )to more concentrated solution (the opposite), against (up) the concentration gradient.

What factors can affect rate of diffusion?

• Temperature

• Steepness of concentration gradient

• Surface Area

What is SA:V and how is it used?

SA:V is surface area to volume ratio and is used in adaptations as the higher SA:V or the higher surface area there is whilst not volume, is more efficient at exchanging substances

What factors increase the effectiveness of a gas exchange surface?

• Large surface area

• Short diffusion path

• Efficient blood supply

• Ventilation (in animals

What is an isotonic solution?

An isotonic solution is a solution that has the same concentration of solutes and water as the inside of a cell.

What is a hypertonic solution?

A hypertonic solution is a solution that has a higher concentration of solutes and a lower concentration of water than the inside of a cell.

What is a hypotonic solution?

A hypotonic solution is a solution with a lower concentration of solutes (like salt or sugar) and a higher concentration of water than the inside of a cell.

How is the small intestine adapted for exchange of materials?

• Villi help with a higher SA:V ratio

• Plenty of capillaries form a steep concentration gradient

How are fish gills adapted for exchange of materials?

• Gill filaments and lamellae hugely increase surface area

• Water flows over the gills opposite to blood flow so blood meets water with a higher oxygen concentration, meaning there is a steeper gradient

How are root hair cells adapted for exchange of materials?

• Large surface area due to shape

• Thin cell wall = shorter diffusion distance

• Larger permanent vacuole means a steeper concentration gradient

• Many mitochondria help supply energy for active transport

How are leaf cells adapted for exchange of materials?

• Leaves are broad and flat so more area to absorb light and gases

• Large air spaces let gases diffuse in and out much more easily

• Stomata control when gases diffuse in and out by opening and closing when turgid/flaccid controlled by guard cells

How do plant leaves and stems remain rigid?

Turgor pressure - water moves in by osmosis, causing the vacuole to swell and the cytoplasm to press against the cell wall.

What would happen if a plant cell was put in a very hypertonic solution?

Water moves out of the cell by osmosis and the vacuole and cytoplasm decrease in size. The cell membrane may pull away from the cell wall, causing the cell to become plasmolysed.

What would happen if an animal cell was put in a very hypertonic solution?

Water moves out of the cell, causing it to shrivel up.

What would happen if an animal cell was put in a very hypotonic solution?

Water moves into the cell, causing it to burst.

What would happen if a plant cell was put in a very hypotonic solution?

When a plant cell is placed in a hypotonic solution water moves into the cell by osmosis, causing it to swell and become flaccid.