Topic 1 - Cell Biology

Cell

The basic building blocks of all living things

Eukaryotic Cells

Complex cells with a nucleus and membrane-bound organelles, e.g plants and animal cells

Prokaryotic Cells

a simple, single-celled organism that lacks a nucleus and other membrane-bound organelles, e.g bacteria

What are 3 differences between Eukaryotic and Prokaryotic Cells?

1. Eukaryotic cells have a nucleus whilst Prokaryotic cells do not.

2. Eukaryotic cells have a mitochondria

What to do both Plants and animal cells both have?

Nucleus, Cytoplasm, Cell Membrane, Mitochondria, Ribosomes

What do Plants cells have but animals cells don't?

Cell wall, Permanent Vacuole, Chloroplasts

Nucleus

Contains genetic material, controls cell activities.

Cytoplasm

Substance where most chemical reaction happens.

Cell Membrane

Holds the cell together and controls what goes in and out

Mitochondria

Where most of the reactions for aerobic respiration happen, for energy

Ribosomes

Where proteins are made in the cell.

Cell wall

Rigid outer layer, made of cellulose-supports and strengthens the cell.

Permanent Vacuole

Contains cell sap, a weak solution of sugar and salts

Chloroplasts

Where photosynthesis occurs,. Contains a green substance called chlorophyll(absorbs the light for photosynthesis).

Bacterial Cells

• Prokaryotic

• Has a cell wall and cell membrane,

• Does not have a nucleus-Instead they have a single circular strand of DNA that floats freely in the cytoplasm. May contain 1 or more ring of DNA called plasmids

• Contain ribosomes and no other organelle(no chloroplast or mitochondria)

• And are much smaller then plant and animal cells

Microscopes

Devices that produce magnified images of structures that are too small to see with the naked eye.

1. Prepare the Onion Sample – Peel off a thin epidermal layer using forceps.

2. Mount on Slide – Place the tissue flat on a slide with a drop of water. Add 2 drops of iodine stain.

3. Place Cover Slip – Lower the cover slip at an angle using forceps to avoid air bubbles. Remove excess stain with paper towels.

4. Set Up Microscope – Select a low power objective and use the coarse adjustment knob to raise the stage close to the objective.

5. Focus the Image – Look through the eyepiece, slowly lower the stage until the image is clear. Switch to high power and fine-tune focus.

6. Draw & Record – Make a labeled drawing of cells, noting key features and magnification. Repeat with a prepared slide.

Electron microscope

Has a higher magnification and higher resolution than light microscopes but is more expensive,

Lets us see internal structures like mitochondria.

Formula for Magnification

Magnification = image size / real size

Specialised Cells

Cells that are adapted to perform a specific function, such as sperm cells

Differentiation

Process in which cells become specialized for its function

What is the function of Sperm Cell and how is it adapted for it?

Function-To go from the male DNA to the female DNA.

Adapted-Long tail, streamlined head to help swim to the egg

Lots of mitochondria for its energy.

Carries enzymes in its head to digest through egg cell membrane.

What is the function of Nerve Cell and how is it adapted for it?

Function- Carry electric signals from one part of the body to another.

Adapted-Long cells(covers more distance), has branched connections at their ends.

What is the function of Muscle Cell and how is it adapted for it?

Function-to contract quickly

Adaption-Long cells (more space to contract), contains lots of mitochondria for energy for contraction

What is the function of Root Hair Cell and how is it adapted for it?

Function-Absorbing Water and Minerals

Adaption-Long root hair cells so they have a large surface area to volume ratio, which increases the rate of water absorption

What is the function of Phloem and Xylem Cell and how is it adapted for it?

Function-transporting substances

Adaption-Xylem cells are hollow, and Phloem have few subcellular structures so substances can flow through.

Chromosomes

Coiled up lengths of DNA molecules.

Humans have 23 pairs of chromosome.

Mitosis

Cell division producing two identical cells.

1. The cell grows and replicates its subcellular structures (e.g., mitochondria, ribosomes).

2. The DNA duplicates, forming X-shaped chromosomes, each with identical copies.

3. The nuclear membrane breaks down, and chromosomes line up at the cell’s center.

4. Fibres pull chromosome arms to opposite ends, and new

5. The cytoplasm and membrane divide, producing two identical daughter cells with the same DNA.

Binary Fission

How prokaryotic cells replicate

1. The genetic material stored in the circular DNA and plasmids get replicated.

2. The cell starts to expand, and the circular DNA moves to opposite poles of the cell.

3. The cytoplasm divides, and cell walls form around the new cells.

4. Two new daughter cells form, each containing a copy of the circular DNA and a variable number of plasmids.

Culturing Microorganisms

Growing bacteria for research and testing.

1. Spray the bench with disinfectant and wipe dry with paper towels. Mark the bottom of the agar plate with 3 segments, a dot in each, and your initials, date, and bacteria name.

2. Wash hands, place antiseptics on filter paper discs, and use forceps to place each disc on the agar plate. Tape the lid securely but loosely enough for oxygen to reach the bacteria.

3. Incubate the plate at 25°C for 48 hours.

4. Measure the diameter of the clear zones after 48 hours, record results, and calculate the area using pi r squared.

Aseptic Technique

Methods to prevent contamination in cultures.

Zones of Inhibition

Clear areas around antibiotics in bacterial cultures.

Use A = π r² to calculate

Stem Cells

Undifferentiated cells capable of differentiating into any cell..

• Plant stem cell - Found in meristem, can differentiate into any plant cell.

• Adult Stem Cells - Found in bone marrow, can differentiate into certain types of cells like blood cells.

• Embryonic Stem Cells - Found in early human embryos, can differentiate into any human body cell.

Therapeutic Cloning

Creating stem cells with the same genetic information as the patient, reducing the risk of rejection.

Stem cells for and against

For:

1. Medical Benefits – Can treat diseases like Parkinson’s, diabetes, and spinal injuries.

2. Regenerative Medicine – Can replace damaged tissues and reduce organ transplant shortages.

3. Scientific Research – Helps us understand cell development and disease progression.

Against:

1. Ethical Issues – Using embryonic stem cells involves destroying embryos.

2. Rejection & Risks – Potential for immune rejection or uncontrolled cell growth (tumors).

3. Expensive & Unproven – Some treatments are still experimental and costly.

Diffusion

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.

Diffusion factors

• Bigger the concentration gradient (the difference in concentration), the faster the diffusion rate.

• Higher temperature = Faster diffusion rate as particles have more energy to move around

• The greater the surface area, the faster the rate of diffusion, more space for particles to diffuse across the membrane.

Exchange surfaces

Multicelluar organisms need exchange surfaces for efficient diffusion

• Thin membrane - Short distance to diffuse

• Large SA : V - More space for gases to diffuse

• (in animals) having an efficient blood supply

• (in animals, for gaseous exchange) being ventilated.

Small Intestine

• Lined with villi to increase surface area for quick absorption.

• Single layer of surface cells for short diffusion distance

Lungs

• Contain alveoli for efficient gas exchange.

• Large surface area, moist lining, thin walls, and good blood supply to maintain concentration gradient.

Fish gills

• Water flows over gills, oxygen diffuses into blood, carbon dioxide diffuses out.

• Gill filaments covered in lamellae for large surface area.

• Thin surface cells & capillary network for short diffusion distance.

Leaves and roots

• Leaves:

  • Stomata allow CO₂ in, O₂ & water vapor out.

  • Guard cells control stomata to prevent water loss.

  • Air spaces increase surface area for gas exchange.

• Roots:

  • Root hair cells provide large surface area for absorption.

  • Concentrated cell sap creates steep water potential gradient.

  • Mitochondria support active transport of mineral ions.

Osmosis

Osmosis is the movement of water molecules across a partially permeable membrane, from a region of high water concentration to low. 

Osmosis practical

Method

1. Prepare Potato Cylinders: Use a cork borer to cut 5 cylinders, trim them to 3 cm, and record their initial length & mass.

2. Prepare Solutions: Measure 10 cm³ of different sugar concentrations (including distilled water) into labeled boiling tubes.

3. Immerse Cylinders: Place one potato cylinder in each boiling tube and leave overnight in a test tube rack.

4. Remove & Dry: Take out cylinders, blot dry with paper towels, and record final length & mass.

5. Calculate Changes: Determine percentage changes in mass and length.

6. Plot Graphs: Graph change in mass & length against sugar concentration.

Sources of error

Discs taken from different parts of the potato may have different water potentials. Potato discs may have different surface areas which affect the rate of osmosis.

Risk assessment

Take care when handling cork borer and sharp knife.

Active Transport

The net movement of particles from an area of low concentration to an area of higher concentration against the concentration gradient using energy

• Root Hair Cells: Specialized for absorbing water and minerals. When soil minerals are dilute, active transport moves ions against the concentration gradient using energy from respiration.

• Active Transport in Humans: Used in the small intestine to absorb glucose and amino acids when diffusion is not possible, ensuring nutrients enter the bloodstream for respiration.

Diffusion, Osmosis, and Active Transport comparisons

• Diffusion: Movement of molecules from high to low concentration (passive).

• Osmosis: Movement of water across a partially permeable membrane (passive).

• Active Transport: Movement of molecules from low to high concentration, requiring energy.