4.1 Cell biology

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A patient has CF

Describe how scientists may use stem cells to create healthy lung tissue that will not be rejected by the patient

• Take stem cells from the patient (eg. from bone marrow, skin)

• Remove/change/fix the faulty CF gene

• Create an embryo using these stem cells

• Remove stem cells from the embryo and stimulate them to differentiate into lung cells

Why are there structural differences between types of cells?

The structural differences allow different types of cells to perform specific functions within an organism.

What are the structural differences in cells caused by?

They are controlled by genes in the nucleus - the differences are caused by differential gene expression, as all cells of an organism contain the same genetic material but only express certain genes that determine their unique structure and function.

How do organisms grow?

Their cells must divide. For example in animals, cells divide by mitosis to produce two new identical daughter cells.

What are stem cells and what can doctors use them for?

An undifferentiated cell that is capable of giving rise to many more cells of the same type and from which other cells can arise from differentiation.

Doctors can repair damaged organs by growing new tissues from stem cells.

What are the two classifications of cells? Give examples for each.

Eukaryotic: animal, plant, protist, fungi cells

Prokaryotic: bacteria cells

Define eukaryotic and prokaryotic cells.

Eukaryotic: any cell that contains a nucleus and membrane bound organelles

Prokaryotic: any cell that does not contain a nucleus and membrane bound organelles

Give differences between eukaryotic and prokaryotic cells

Eukaryotic cells have membrane bound organelles and a nucleus, whereas prokaryotes do not. Prokaryotic cells are much smaller.

Where is the genetic material in a prokaryotic (bacterial) cell?

The genetic material is not enclosed in a nucleus; it is a single loop of DNA and there may be one or more small rings of DNA called plasmids

What do the different structures of cells do?

Give cells different functions

Give the prefixes of units of measurements

Centi: 1/100

Milli: 1/1,000 10^-3

Micro: 1/1,000,000 10^-6

Nano: 1,000,000,000 10^-9

What subcellular structures do plants and animals share?

Nucleus

Cell membrane

Cytoplasm

Ribosomes

Mitochondria

What subcellular structures are only in plant cells?

Chloroplasts

Permanent vacuole filled with cell sap

Cell wall

What structures do bacterial cells have?

Cell wall

Cell membrane

Cytoplasm

Single loop of DNA + plasmids

Ribosomes

Function of the nucleus

Contains the genetic material which controls the cell’s activities

Function of the cytoplasm

Site of chemical reactions (contains enzymes)

Function of the cell membrane

Controls the movement of substances into and out of the cell

Function of the mitochondria

Site of aerobic respiration releasing energy for the cell’s functions

Function of the ribosomes

Synthesises proteins

Function of chloroplasts

Contains chlorophyll to absorb the light energy needed for photosynthesis and acts as the site of photosynthesis

Function of the permanent vacuole

Stores water, nutrients and waste products and provides structural support to the cell to keep it rigid

Purpose of the cell wall

Made from cellulose (except from bacterial cells) to provide strength to the cell

How do cells become specialised?

They undergo differentiation: a process where cells gain subcellular structures so that they can be suited to their role

Give three examples of specialised cells in animals

Sperm cells

Nerve cells

Muscle cells

State the purpose of the sperm cell and its adaptations

Purpose: carry the male’s DNA to the egg cell for successful fertilisation

Streamlined head and long tail to aid swimming

Many mitochondria to supply the cell with energy to move

Acrosome has digestive enzymes to break down outer membranes of the egg

State the purpose of nerve cells and its adaptions

Purpose: transmit electrical signals quickly from one place of the body to another

Long axon so the cell can carry the signals along long distances

Lots of dentrites to form connections with other cells

Myelin sheath for insulation for faster impulse conduction

Lots of mitochondria for energy to make neurotransmitters

State the purpose of muscle cells and its adaptations

Specialised to contract quickly to pull bones and cause movement

Special protein filaments that can slide over each other to contract

Lots of mitochondria for energy for contraction

Can store glycogen to to provide glucose for respiration

Give examples of specialised cells in plants

Root hair cells

Xylem cells

Phloem cells

State the purpose and adaptations of root hair cells

To take up water by osmosis and mineral ions by active transport from soil

Large surface area to increase amount it can take in

Lots of mitochondria for active transport

Thin cell wall to provide a short diffusion pathway

Large permanent vacuole containing concentrated cell sap to make water potential of the cell lower than the soil, maintaining a high concentration gradient for osmosis

State the purpose and adaptation of xylem cells

Specialised to transport water and mineral ions up the plant from roots to shoots

Long hollow tubes of dead cells to transport water

Cell walls are strengthened with lignin to allow cells to withstand the pressure from the movement of water

State the purpose and adaptations of phloem cells

Specialised to carry dissolved sugars to all parts of the plant

The cells have sieve plates to allow the movement of substances

Companion cells have lots of mitochondria to release energy for translocation which requires energy

Doesn’t have other organelles to maximise space for transport

How do cells become specialised?

They undergo differentiation which causes some of the genes to be expressed differently (turned on or off) allowing them to produce different proteins allowing the cell to acquire different sub cellular structures for it to carry out specific functions. This means that it has become a specialised cell.

What is the difference between a cell’s ability to differentiate in animal and plant cells

Usually animal cells differentiate early on and then lose this ability

Many plant cells retain the ability to differentiate throughout life

What is the main purpose of cell division in mature animals?

Repair and replacement of cells.

In animal cells, what are the two ways cells can be repaired and replaced?

Through cell division by mitosis

Some specialised cells lose their nucleus and therefore cannot divide, meaning that they can be replaced by adult stem cells which differentiate to form these specialised cells

What are two factors that impact the quality of a microscope?

Magnification

Resolving power (allows cells to be seen in finer detail)

Which type of microscope is better/newer?

An electron microscope has a greater magnification and resolving power than a light microscope

What is the formula for magnification?

Magnification = image size / real size

How do bacterial cells divide?

By binary fission

What do bacterial cells need for optimum binary fission?

Enough nutrients

The right temperature

What can bacteria be grown in?

Nutrient broth

Agar jelly

How does a nucleus contain a cell’s genetic information?

Genetic information is stored in the form of chromosomes which are made up of DNA molecules. Each chromosome carries a large number of genes

What are chromosomes?

Structures found in the nucleus that are made up of DNA molecules, carrying a large number of genes

What are genes?

A gene is a section of DNA that codes for a protein and as a result controls a characteristic

What is the order of genetic information?

Cell

Nucleus

Chromosomes

Genes

How many pairs of chromosomes are there in the human body? How many in total?

23 pairs and 46 in total

What are the only cells that don’t have 46 chromosomes?

Sex cells (gametes) have only 23 chromosomes

What is the purpose of cell division by mitosis?

Growth and development in multicellular organisms

Repair and replacement of cells

Asexual reproduction

What is the cell cycle?

A series of stages that a cell must undergo in order to divide (mitosis is a stage in the cell cycle)

Describe the three stages of the cell cycle:

Stage 1 (interphase): the cell grows and increases its number of sub cellular structures. The DNA replicates to form two copies of each chromosome

Stage 2 (mitosis): chromosomes line up in the middle of the cell and the cell fibres pull each set of chromosomes to either side of the cell

Stage 3 (cytokinesis): the cytoplasm and cell membrane divides to form two identical daughter cells

Define 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 conditions can treatment with stem cells help to treat?

Diabetes and paralysis

Give one unconventional use of mitosis?

Asexual reproduction; it only involves one organism to to produce offspring an organism simply replicates its own cells by mitosis

Give three types of stem cells

Embryonic stem cells

Adult stem cells

Meristem tissue

Describe what embryonic cells are and how they are used

These are stem cells made from human embryos that can differentiate into any type of cell

Scientists can clone these cells by culturing them and direct them to differentiate into almost any cell in the body

Can be used to produce insulin resisting cells (to treat diabetes) or new nerve cells (to treat paralysis)

What are adult stem cells and give their function and how they are used

They are stem cells found in bone marrow that can differentiate throughout a lifetime

They can be used to form blood cells

What are meristem cells and give their function and how they are used

Stem cells are found in the tips of roots and shoots can and differentiate into any type of plant cell; they retain this ability throughout a plant’s lifetime

They can be used to make clones of plants to save a rare plant from extinction or produce plants with desirable features

What is therapeutic cloning?

An embryo is produced with the same genes as the patient. The embryo produced could then be harvested to obtain embryonic stem cells with the same genetic material as the patient, meaning that they would not be rejected. These cells could be grown into any cells that the patient needed, such as new tissues or organs

What are uses of meristem tissue?

Stem cells from meristems in plants can be used to produce clones of plants quickly and economically:

Rare species can be cloned to prevent extinction

Crop plants with special features (such as disease resistance) can be cloned to produce large numbers of identical plants for farmers

Give the advantages and disadvantages of the use of stem cells in medical research and treatments

Advantages:

Can be used to treat many diseases, which saves lives

Stem cell research can be used in other research to aid discovery of treatment for other diseases

Stem cell research may occur illegally if banned, so it is better to legalise and regulate it

Unwanted embryos from fertility clinics could be used as they would otherwise be discarded

Disadvantageous:

Removal of stem cells causes destruction of embryos, so people believe it is killing life

If the sample of stem cells contained a virus, it could infect the patient

It is difficult to control the stem cells to form the desired cells needed

Religious or ethical objections because it interferes with the natural process of reproduction

Money and time could be better spent in other areas of medicine

Define diffusion

The spreading out of particles resulting in a net movement from an area of higher concentration to lower concentration. This process does not require energy

Give examples of diffusion in the human body

Oxygen and carbon dioxide during gas exchange

Urea from cells into the blood plasma for excretion in the kidney

Give the factors that affect the rate of diffusion

Concentration gradient

Temperature

Surface area of membrane

How does concentration gradient affect the rate of diffusion?

The greater the difference in concentration, the faster the rate of diffusion.

This is because more particles are randomly moving along the concentration than against it

Explain how temperature affects the rate of diffusion

The greater the temperature of particles, the greater the movement of particles resulting in them moving faster and colliding more frequently which increases the rate of diffusion

Explain how the surface area of the membrane increases the rate of diffusion

The greater the surface area the more space for particles to move through resulting in a faster rate of diffusion

What is the surface area to volume ratio of an organism

The size of the surface area of an organism compared to its volume

Explain why diffusion is a sufficient method of transport for unicellular organisms

They have a large surface area to volume ratio. They also have low metabolic demands, so diffusion is sufficient

Explain why multicellular organisms need for exchange surfaces and antransport systems

They have lower surface area to volume ratios and greater metabolic demands so they need exchange surfaces and a transport system

Explain how the lungs are adapted for exchanging materials

The lungs have alveoli to increase their surface area

They have a high blood supply to maintain a high concentration gradient

How is the small intestine adapted for transport of materials?

They have villi and microvilli to increase their surface area

It has a thin membrane to provide a short diffusion pathway

It has a high blood supply to maintain a high concentration gradient

How are gills adapted for transport?

The gills have filaments which give it a high surface area

The gill filaments have thin cell membrane giving it a short diffusion pathway

The gill filaments have a high blood supply to maintain a high concentration gradient

How are roots adapted for transport of materials?

Root hair cells to increase their surface area surface area

Root hair cells have large vacuoles to maintain a concentration gradient

How are leaves adapted for diffusion?

They are flat to increase the surface area

Thin cell membrane to decrease diffusion pathway

Stomata and guard cells which allow/ control the movement of gases into and out of the plant

What are the adaptations of exchange surfaces for efficient exchange?

Large surface area

Having a thin membrane

Having an efficient blood supply

Being ventilated

Define osmosis

The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane. This process does not require energy

Water moves from an area of high water potential (high concentration of water) to low water potential

Define isotonic

When the concentration of sugars in a cell is the same concentration as the solution it is in meaning there will be no movement of water

Define hypertonic

If the concentration of sugar in the cell is less than the concentration of sugar in the solution the solution is said to be hypertonic to the cell, meaning that water moves out of the cell

Define hypotonic

If the concentration of sugar in the solution that the cell is in is less than the concentration of sugar in the cell the solution is said to be hypertonic to the cell, and water will move into the cell

What happens if animal cells are placed in hypertonic and hypotonic solutions

Hypertonic: water moves out of the cell and the cell will become shrivelled

Hypotonic: water moves into the cell and the cell may burst

What happens if plant cells are placed in hypertonic and hypotonic solutions?

Hypertonic: water will move out of the cell. This causes the cell to shrink and become flaccid. Eventually the cell membrane will move away from the cell wall (plasmolysis) and the cell will die

Hypotonic: water will move into the cell making it turgid

Define active transport

Movement of substances from a dilute solution to a concentrated solution, against a concentration gradient. This process requires energy

Give an example of active transport in plants

Root hairs take up water and mineral ions from the soil which requires energy from respiration. They have lots of mitochondria for this

Give an example of active transport in animals

Glucose and amino acids are moved from the gut into the bloodstream

Explain the differences between diffusion, osmosis and active transport

Diffusion: spreading out of particles, resulting in a net movement of particles, from an area of higher concentration to lower concentration. This process does not require energy

Osmosis: the movement of water from a dilute solution to a concentrated solution through a partially permeable membrane. This process does not require energy

Active transport: the movement of substances from a low concentration of substance to a higher concentration of substance, against a concentration gradient. This process requires energy