Biology chapter 1 - cell biology

Includes: Cells, microscopy, cell differentiation and specialisation, chromosomes and mitosis, binary fission, culturing microorganisms, stem cells, diffusion, osmosis, active transport, exchange surfaces, exchanging substances

differences of prokaryotic vs eukaryotic cells

Prokaryotic:

• small and simple

• genetic material isn’t enclosed in a nucleus

• very few organelles

• unicellular

Eukaryotic cells:

• large and complex

• genetic material is enclosed in a nucleus

• many organelles

• multicelluar

similarities between prokaryotic and eukaryotic cells

They both have a cell membrane

They both have ribosomes

They both contain DNA

Explain each function of the organelles from an animal cell:

Nucleus

Cytoplasm

Cell membrane

Mitochondria

Ribosomes

Nucleus - contains genetic material that controls the activities of the cell

Cytoplasm - gel-like substance where most of the chemical reactions happen. It also contains enzymes that control the chemical reactions

Cell membrane - holds the cell together and controls the molecules which go in and out of the cell

Mitochondria - these are where most of the reactions for aerobic respiration take place.

Ribosomes - site of protein synthesis

Explain the function of the organelles from a plant cell:

Cell wall

Vacuoles

Chloroplasts

Cell wall - made of cellulose. It supports the cell and strengthens it

Vacuole - contains cell sap, a weak solution of sugar and salts. It also helps give the plant cell its shape

Chloroplasts - where photosynthesis occurs, which makes food for the plant as it contains chlorophyll which absorbs light needed for photosynthesis.

Differences between a light microscope and an electron microscope

Light microscopes use light and lenses to form an image while electron microscopes use electrons.

Electron microscopes use a higher resolution which gives a sharper image

Electron microscopes have a higher magnification which allows us to see much smaller things in more detail.

formula for magnification

Magnification = image size/real size

How to prepare a slide to view an onion cell

1. Using a pipette add a drop of water to the middle of a clean slide

2. Cut up the onion and separate it out into layers by using forceps to peel off the top epidermal tissue from the bottom of an onion

3. Place the epidermal tissue into the water on the slide

4. Add a drop of iodine solution to the epidermal tissue on the slide, this will stain the epidermal tissue to make it easier to see under the microscope

5. Then place a cover slip over the specimen but at a 45 degree angle so that no air bubbles get trapped in it.

label the microscope

answers:

What is cell differentiation

Is the process by which a cell changes to become specialised for specific function

How is the sperm cell specialised for reproduction?

The function of a sperm is to get the male DNA to the female DNA (ovum). It has a long tail and a streamlined head to help it swim to the egg. There are lots of mitochondria in the cell to provide the energy needed. It also carries enzymes in its head to digest through the egg cell membrane. It contains their genetic information in the nucleus, however it only contains half the genetic information of a normal adult cell.

How is the nerve cell specialised for rapid signalling?

The function of the nerve cell is to carry electrical signals from one part of the body to another. These cells have a long axon so they can cover more distance and carry electrical impulses. The axon is covered in myelin which insulates the axon and speeds up the transmission of nerve impulses. They also have synapses at their ends which allow impulses to pass from one nerve cell to another. Dendrites increase the surface area so that other nerve cells can connect more easily.

How is the muscle cell specialised for contraction

The function of a muscle cell is to contract quickly, they contain protein fibres which can change their length allowing them to contract. These cells are long so they have space to contract and contain many mitochondria to generate the energy needed for contraction. They work together to form muscle tissue.

How is the root hair cell specialised for absorbing water and minerals?

Root hair cell are cells on the surface of plant roots which grow into hairs. This gives the plant a big surface area for absorbing water and mineral ions from the soil. They also don’t contain chloroplasts because they are underground, meaning that they don’t photosynthesise.

How is the phloem and xylem cells specialised for transporting substances?

Phloem:

• Tubes carry dissolved sugars up and down the plant

• Contains phloem vessel cells which have no nucleus and only limited cytoplasm. End walls of the vessel cells have pores called sieve plates. These two features allow dissolved sugars to move through the cell interior

• Each phloem vessel cell has a companion cell connected by pores. The mitochondria in the companion cell provide energy to the phloem vessel cell

Xylem:

• They are found in the plant stem and form long tubes which carries water and dissolved minerals from the roots to the leaves

• Have very thick walls containing lignin which provides support to the plant. This also causes the xylem to die.

• The end walls between the cells have broken down so the cells have now formed a long tube

• No nucleus, cytoplasm, vacuole, or chloroplasts.

• Have no internal structure at all making it easier for water and minerals to flow

What is mitosis and how is it used?

Mitosis is the stage of the cell cycle when the cell divides. Multicellular organisms use mitosis to grow or replace cells that have been damaged.

Growth and DNA replication of the cell cycle

1. In a cell that’s not dividing the DNA is all spread out in long strings

2. Before it divides, the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes

3. It then duplicates its DNA so there is one copy for each cell.

Stages of the cell cycle (summary)

Stage 1 - the longest stage, building cell mass and replicating DNA

Stage 2 - Mitosis: nuclear division, nucleus divides into two

Stage 3 - Cytokinesis: cell splits into two, producing two daughter cells

Stages of mitosis

1. The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell

2. Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells - the nucleus has divided.

3. Lastly the cytoplasm and cell membrane divide.

The cell has now produced two new daughter cells. The daughter cells contain exactly the same DNA - they’re identical to each other and to the parent cell.

How is a cell controlled by genes?

Inside a cell there is a chromosome in a nucleus with a DNA. The chromosome never leaves the nucleus. mRNA go into the nucleus and receive directions from one section of the DNA. mRNA take the directions to parts of the cell. These directions tell the ribosomes in the cell to make certain proteins. Each part of the organelle makes something different. A different cell has a different DNA, and so it makes different end proteins.

Difference between a plant and animal cell

Plant:

• Have a regular shape

• have a cell wall

• contain chloroplasts which contain chlorophyll for photosynthesis

Animal:

• irregular shape

• Don’t have a cell wall

• don’t have a large permanent vauole

How to use a light microscope to view a prepared slide

• Place the slide onto the stage using the clips to hold the slide in place

• Select the lowest power objective lens which is usually 4x

• Position the objective lens so it almost touches the microscope slide. To do that slowly turn the coarse focussing dial

• Look at the microscope from the side while adjusting the position of the objective lens. When the objective lens almost touches the slide stop turning the dial.

• Then look down through the eyepiece

• Slowly turn the coarse focussing dial, to increase the distance between the objective lens and the slide until the cells come into focus

• Then use the fine focussing dial to make the cells clearer

How to calculate total magnification

Magnification of the eyepiece lens * magnification of the objective lens

How do bacteria multiply?

Simple cell division.

One bacterial cell splits into two bacterial cells - binary fission

How can binary fission occur in bacteria?

Bacteria can carry out binary fission once every twenty minutes as long as they have enough nutrients and the temperature is suitable

Formula for number of bacteria present after a given time

2ⁿ

n = number of rounds of division

e.g. a type of bacterium divides every twenty minutes. Calculate the number of bacteria present after three hours.

3 hours = 180

180/20 = 9 rounds of division

number of bacteria = 2⁹ = 512

How to avoid contamination when using a petri dish

• Sterilise all petri dishes, bacterial nutrient broth and agar to kill any unwanted bacteria or microorganisms and prevent contamination

• Sterilise the inoculating loop by passing it through a Bunsen burner flame

• Attach the lid of the petri dish using adhesive tape to top the lid from falling off and unwanted microorganisms entering

• Place the agar plate upside down into an incubator to stop moisture from dripping down onto the bacteria and disrupting the colonies

How to choose the right temperature of culturing bacteria on agar jelly

In school labs, we incubate bacteria at 25^oC to reduce the chances that harmful bacteria will grow

Required practical:

Effect of antibiotics on bacterial growth

1. Clean the bench with disinfectant solution which kills microorganisms that could contaminate our culture

2. Sterilise an inoculating loop by passing it through a Bunsen burner flame

3. Open a sterile agar gel plate near a Bunsen burner flame which kills bacteria in the air

4. Use the loop to spread the chosen bacteria evenly over the plate

5. Place sterile filter paper disc containing antibiotic onto the plate

6. Incubate the plate at 25^oC

What is around the antibiotic discs

Around the antibiotic discs we have a region where the bacteria have not grown which is called the zone of inhibition

formula for the area of the zone of inhibition

area of zone of inhibition = pi x r²

What is a stem cell

An undifferentiated cell which can give rise to more cells of the same type and can differentiate to form other types of cells

Bone marrow transplant steps

1. Leukaemia is a cancer of the bone marrow

2. To treat this the patient’s existing bone marrow is destroyed using radiation

3. The patient then receives a transplant of bone marrow from a donor

4. The stem cells in the bone marrow now divide and form new bone marrow. They also differentiate and form blood cells

Problems with bone marrow transplant

• The donor has to be compatible with the patient otherwise the white blood cells produced by the donated bone marrow could attack the patient’s body

• There is a risk that viruses can be passed from the donor to the patient

Therapeutic cloning steps

• In therapeutic cloning an embryo is produced with the same genes as the patient. So, stem cells from the embryo can be transplanted into the patient without being rejected by the patients immune system

• Once inside the patient, the stem cells can then differentiate to replace cells which have stopped working correctly

Benefits and issues with therapeutic cloning

Can be useful for a range of medical conditions such as diabetes or paralysis

Some people have ethical or religious objections to the procedure

What is meant by diffusion

Diffusion is the spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration.

Factors that effect rate of diffusion

• Difference in concentrations - The difference in concentration is also called the concentration gradient. The greater to concentration gradient, the faster diffusion takes place.

• Temperature - The higher the temperature the greater the rate of diffusion because the particles have more kinetic energy and are moving faster.

• Surface area of the membrane - The larger the surface area of the cell membrane, the greater the rate of diffusion

What is surface area to volume ratio

When something has a large surface area for their volume

How to calculate surface area to volume ratio

1. Find the total surface area

2. Find the total volume

3. Put the values into a ratio

4. Simplify the ratio

Trend in the surface area to volume ratio + their problems

As organisms get larger the surface area to volume ratio falls sharply. This presents a huge problem for multicellular organisms because their surface area is not large enough for their volume.

How do fish get their oxygen?

The oxygen-rich water passes into the mouth. It then flows over gills, where the oxygen is transported into the blood stream. The gills are covered in a very large number of fine filaments where gases pass in and out of the blood. Deoxygenated blood passes into the filament. Oxygen diffuses from the water into the blood. Oxygenated blood returns to body.

Three adaptations of filaments

• Massive surface area

• thin membrane to provide a short diffusion pathway

• efficient blood supply to take the oxygenated blood away. This ensures that the concentration gradient is always high

• These adaptations make diffusion efficient as possible

What is meant by osmosis

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

What is meant by a high or low concentration of water

Dilute solutions contain a high concentration of water (high water potential)

Concentrated solutions contain a low concentration of water

What does a partially permeable membrane mean

Membranes that allow some molecules to pass through but not all molecules

effects of osmosis on animal cells

The water will diffuse into the animal cell and cause it to expand or even burst

If an animal cell is placed in a very concentrated solution, the water will move out of the cell by osmosis and the cell with shrink.

effect of osmosis on plant cells

If a plant cell is placed in water, then water will move into the cell via osmosis and expand. The cell wall prevents the plant cell from bursting. Instead the cell becomes swollen also known as turgid.

If a plant cell is placed in a concentrated solution the water moves out of the plant cell causing it to shrink which is also known as flaccid.

Potato experiment - osmosis

1. Peel the potato because the skin can affect osmosis

2. Use a cork borer to produce 3 cylinders of potato. Using the cork borer makes all the cylinders the same diameter

3. Use a scalpel to trim the cylinders to the same length around 3cm

4. Measure the length of each cylinder using a ruler and the mass of each cylinder to balance

5. Place each cylinder into a test tube. Add 10cm³ to a 0.5 molar sugar solution to the first test tube

6. Then add a 10cm³ of 0.25 molar sugar solution to the second test tube and 10cm³ of distilled water to the third test tube

7. Leave the potato cylinders overnight to allow osmosis to take place

8. Remove the potato cylinders and gentry roll them on paper towel to remove any surface moisture

9. Measure the length and mass of the cylinders again

10. The calculate the percentage change.

How to calculate percentage change

(change in value/original value) x 100

Results of the potato osmosis experiment

• In water, the potato cylinder gains mass as water moves into it by osmosis

• In concentrated sugar solution, the cylinder loses mass as water moves out by osmosis

• Where the line on the graph crosses the x-axis there is no change in mass because the concentration outside the cell is the same as the concentration inside the cell so no overall osmosis takes place.

What is meant by active transport?

Active transport moves substances from a more dilute solution to a more concentrated solution (against the concentration gradient). This requires energy from respiration

Examples of active transport in animal and plant cells

plant cells - ions in root hair cell

animal cells - lumen of small intestines (sugars to the blood stream)