Biology: Topic 1: Cell biology

What are cells?

• All living things are made up of cells

• Cells can be either prokaryotic or eukaryotic

What are eukaryotic cells?

• Complex

• Have a cell membrane, cytoplasm and genetic material enclosed in a nucleus

• Animal and plant cells

What are eukaryotes?

Organisms that are made up of eukaryotic cells (multiple)

What are prokaryotic cells?

• Smaller and simpler than eukaryotic (e.g. bacteria)

• Genetic material is not enclosed

What are prokaryotes?

Organisms made up of a prokaryotic cell (single-celled)

What are subcellular structures?

The different parts of a cell

What are the parts of an animal cell?

• Nucleus

• Cytoplasm

• Cell membrane

• Mitochondria

• Ribosomes

What are the parts of a plant cell?

• Nucleus

• Cytoplasm

• Cell membrane

• Mitochondria

• Ribosomes

• Cell wall

• Vacuole

• Chloroplasts

What is the nucleus?

• Contains genetic material (DNA) that controls the activities of the cell

• Has the information needed to produce new cells

What is the cytoplasm?

• Gel-like substance where most of the chemical reactions happen

• Contains enzymes which control these chemical reactions

What is the cell membrane?

• Holds the cell together and controls what goes in and out

• Creates a barrier between the cell and the outside world 

What are mitochondria?

• Where most of the reactions for aerobic respiration take place which release energy

• Powerhouse of the cell and provides energy for it

What are ribosomes?

• Carry out protein synthesis (this is where proteins are made in the cell)

• Read DNA from the nucleus and build protein using these instructions

What is the cell wall?

• Rigid and made of cellulose

• Supports the cell and strengthens it

• Helps the cell maintain its shape

What is the vacuole?

• Permanent and contains cell sap, a weak solution of sugar and salts

• Keeps the cell turgid

What are chloroplasts?

• Contains the green pigment chlorophyll which absorbs light for photosynthesis

• Only found in some parts of the plant (green parts)

What subcellular structure do plant and algal cells also have?

• (e.g. seaweed)

• a cell wall made of cellulose, which strengthens the cell

What are the parts of a bacterial cell?

• Cell membrane

• Cell wall

• Plasmids

• Genetic material

• Ribosomes

• Cytoplasm

How are bacterial cells different to animal and plant cells?

• Smaller

• Don’t have chloroplasts, mitochondria or a true nucleus

What is genetic material?

• A single circular strand/ loop of DNA that floats freely in the cytoplasm

What is a plasmid?

• Small loop of DNA

• Often codes for traits to do with protection like resistance against drugs

What do microscopes help us do?

Let us see things we can’t see with the naked eye

How do light microscopes work?

Use light and lenses to form an image of a specimen and magnify it

What can you see through a light microscope?

Individual cells and large subcellular structures like nuclei

How do electron microscopes work?

Use electrons instead of light to form an image

How are electron microscopes different to light microscopes?

• They have a higher magnification and resolving power

What can you see through an electron microscope?

Subcellular structures

Why are electron microscopes useful?

• Let us study things in more detail

• (e.g. the internal structure of mitochondria and chloroplasts)

What is the resolution of an image?

The ability to distinguish between two points

What does a higher revolution give?

A sharper image

Magnification formula

Magnification = image size / actual size
I = AM
image and actual can be in any units, as long as they are the same

What is differentiation?

The process by which a cell changes to become specialised for its job

Describe cell differentiation

• As cells change, they develop different subcellular structures and turn into different types of cells

• This allows them to carry out specific functions

• Most differentiation occurs as an organism develops

What is the difference between differentiation in plant and animals cells?

Animal cells

• Most types of animal cells differentiate at an early stage 

• In mature animals, cell sub-division is mainly restricted to repair and replacement of cells, such as skin or blood cells

Plant cells

• Many types of plant cells retain the ability to differentiate throughout life

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 certain other cells can arise from differentiation

(Can divide to produce lots more undifferentiated cells
They can differentiate into different types of cell, depending on what instructions they’re given)

What are sperm cells specialised for?

Reproduction

What is the function of sperm cells?

Function is to get the male DNA to the female DNA

What are the adaptations of sperm cells?

• Long tail and a streamline head to help it swim to the egg

• Lots of mitochondria in the cell to provide the energy needed

• Carries enzymes in its head to digest through the egg cell membrane

What are nerve cells specialised for?

Rapid signalling

What is the function of a nerve cell?

To carry electrical signals from one part of the body to another

What are the adaptations of a nerve cell?

• Long (to cover more distance)

• Have branched connections at their ends to connect to other nerve cells and form a network throughout the body

What are muscle cells specialised for?

Contraction

What is the function of muscle cells?

To contract quickly

What are the adaptations of muscle cells?

• Long (so that they have space to contract) 

• Contain a lot of mitochondria to release the energy needed for contractions

What are root hair cells?

Cells on the surface of plant roots, which grow into long ‘hairs’ that stick out into the soil

What are root hair cells specialised for?

Absorbing water and minerals

What are the adaptations of root hair cells?

Root hairs give the plant a big surface area for absorbing water and mineral ions from the soil

What are phloem and xylem cells specialised for?

Transporting substances around the plant

What do xylem and phloem cells form?

Xylem and phloem tubes

Nuclei in human cells

• Most cells in the body have a nucleus

• Contains genetic material in the form of chromosomes

What are chromosomes?

Coiled up lengths of DNA molecules

Where are genes found and what do they do?

• Each chromosome carries a large number of genes

• Different genes control the development of different characteristics such as hair colour

How many chromosomes are there in the human body?

23 pairs

How many copies of each chromosome do body cells normally have?

2

Where does each chromosome come from?

One from the organism’s mother and one from its father

How many copies of each chromosome do humans have?

Humans have two copies of chromosome 1, two of chromosome 2 and so on

What is the cell cycle?

Body cells in multicellular organisms divide to produce new cells as part of a series of stages

What are the stages of the cell cycle?

1. Interphase

2. Mitosis

3. Cytokenisis

What happens in the interphase stage of the cell cycle?

• Cell organelles replicate - number of subcellular structures doubles

• DNA replicates to form two copies of each chromosome

• Further growth occurs

• The DNA is checked for mutations and mistakes made

What happens when DNA replicates to form two copies of each chromosome?

• X shaped chromosomes are formed

  • Each arm of the chromosome is an exact duplicate of the other 

What happens in the mitosis stage of the cell cycle?

• Chromosomes line up at the centre of the cell 

• Spindle-fibres form and pull the chromosomes apart to each pole of the cell

What happens in the cytokinesis stage of the cell cycle?

• Membranes form around each of the new sets of chromosomes

• These become the nuclei of the two cells

• The cytoplasm and cell membrane separates to give 2 new identical daughter cells with the same number of chromosomes as the parent cell

What is cell division by mitosis important for?

The growth and development of multicellular organisms

What do multicellular organisms use mitosis for?

To grow or replace damaged cells

What does the cell cycle result in?

2 new identical daughter cells with the same number of chromosomes as the parent cell

What is binary fission?

When a bacteria cell splits in two

What happens in the binary fission process?

1. Circular DNA and plasmids replicate 

2. Cell gets bigger and the circular DNA strands move to the poles of the cell

3. Cytoplasm begins to divide and new cell walls begin to form

4. Cytoplasm divides and two daughter cells are produced 

5. Each cell has one copy of the circular DNA but can have a variable number of plasmids 

What conditions are required for bacteria to grow quickly?

• warmth

• oxygen

• water

• lots of nutrients

How long can E.coli bacteria take to replicate?

As little as 20 minutes in the right environment

What happens if the conditions are unfavourable for the bacteria?

The cells will stop dividing and will eventually begin to die

What is the mean division time for bacteria?

The average amount of time it takes for one bacterial cell to divide into two

Where are embryonic stem cells found?

Early human embryos

Why are embryonic stem cells exciting for doctors and medical researching?

They have the potential to turn into any kind of cell at all

Where are stem cells found in adults?

Only certain places, like bone marrow

What types of cells can bone marrow stem cells differentiate into?

Only certain ones like blood cells

How can stem cells from embryos and bone marrow produce clones?

They can be grown in a lab to produce clones (genetically identical cells)

What can close from stem cells be made to do?

Differentiate into specialised cells to use in medicine or research

How can bone marrow cells be used to cure disease?

Stem cells transferred from the bone marrow of a health person can replace faulty blood cells in the patient who receives them

How can embryonic stem cells be used to cure disease?

To replace faulty cells, e.g.:

• insulin-producing cells for people with diabetes

• nerve cells for people paralysed by spinal injuries and so on

How does therapeutic cloning work?

An embryo could be made to have the same genetic information as the patient

What makes therapeutic cloning safe?

• Stem cells produced from it would contain the same genes as the person

• So wouldn’t be rejected in the patient’s body

What are the risks involved using stem cells in medicine?

Stem cells grown in the lab could be contaminated with a virus which could be passed on to the patient and so make them sicker

What are the reasons against stem cell research?

Some people feel human embryos shouldn’t be used for experiments because:

• Each one is a potential human life

• They think scientists should concentrate more on finding and developing other sources of stem cells so people can be helped without having to use embryos 

• Religious objections

What are the reasons for stem cell research?

Some people think that:

• Curing existing patients who are suffering is more important than the rights of embryos

• The embryos used in the research are usually unwanted ones from fertility clinics which, if they weren’t used in research would probably just be destroyed

Where is stem cell research legal?

• UK - allowed as long as it follows strict guidelines

• Banned in some countries

Where are stem cells found in plants?

The meristems (parts of the plant where growth occurs)

What can meristem tissue differentiate into?

• (Throughout the plant’s entire life)

• Into any type of plant cell

Why are meristem cells used to produce clones of the whole plants?

They can produce whole plants quickly and cheaply 

How can stem cells be used to produce identical plants?

• Can be used to grow more plants of rare species to prevent them from being wiped out

• Can be used to grow crops of identical plants that have desired features for farmers (e.g. disease resistance)

What is diffusion?

The net movement of particles from an area of high concentration to an area of low concentration, down the concentration gradient

What are two examples of substances transported in and out of cells by diffusion?

• Oxygen and carbon dioxide in gas exchange

• The waste product urea from cells into the blood plasma for excretion in the kidney

What substances does diffusion happen with?

Solutions and gases - the particles are free to move about randomly 

What is the simplest type of diffusion?

When different gases through each other

What are the 3 factors affecting diffusion?

1. Concentration gradient

2. Temperature

3. Surface area

How does the concentration gradient affect diffusion?

The bigger the concentration gradient, the faster the diffusion rate

How does surface area affect diffusion?

A larger surface area gives a faster diffusion rate because there is more space for diffusion

How does temperature affect diffusion?

A higher temperature will give a faster diffusion rate because the particles have more energy, so move around faster

What do cell membranes do in terms of diffusion?

Hold the cell together but let things in and out as well

What types of molecules can diffuse through cell membranes?

Only small molecules

(Big molecules like starch and proteins can’t fit through the membrane)

Give 4 examples of molecules that can diffuse through cell membranes

• Oxygen

• Glucose

• Amino acids

• Water