All-In-One: Cell Biology (P1)

Eukaryotic cells

Cells that contain membrane bound-organelles and a nucleus containing genetic material.

Prokaryotic cells

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

Genetic information in prokaryotic cells

Stored free within the cytoplasm as chromosomal DNA and plasmid DNA.

Plasmids

Small, circular loops of DNA found free in the cytoplasm, carrying genes that provide genetic advantages such as antibiotic resistance.

Components of plant and animal cells

Nucleus, Cytoplasm, Cell membrane, Mitochondria, Ribosomes.

Additional components found in plant cells (difference)

Chloroplasts, Permanent vacuole, Cell wall.

Function of the nucleus

Contains DNA and controls cellular activities.

Structure of the cytoplasm

Fluid component of the cell that contains organelles, enzymes, and dissolved ions and nutrients.

Function of the cytoplasm

Site of cellular reactions and transport medium.

Function of the cell membrane

Controls the entry and exit of materials into and out of the cell.

Function of the mitochondria

Site of later stages of aerobic respiration in which ATP is produced.

Function of the ribosomes

Joins amino acids in a specific order during translation for the synthesis of proteins.

What is plant cell wall made of?

Cellulose.

Function of the plant cell wall

Provides structure and support to the plant cell.

Permanent vacuole contents

Cell sap (a solution of salts, sugars and organic acids).

Function of the permanent vacuole

Supports the cell, maintaining its turgidity.

Function of chloroplasts

Site of photosynthesis.

Adaptation of sperm cells in animals

- Haploid nucleus contains genetic information

- Tail enables movement

- High amounts of mitochondria to provide energy for tail movement

Adaptation of nerve cells in animals

- Long axon allows electrical impulses to be transmitted all over the body

- Dendrites connect to and receive impulses from other nerve cells, muscles, and glands

- Myelin sheath insulates the axon and speeds up transmission of impulses.

Adaptation of muscle cells in animals

- Arrangement of protein filaments allows them to slide over each other to produce muscle contraction

- Mitochondria provide energy for muscle contraction

- Merged cells in skeletal muscle allow muscle fibre contraction in unison.

Adaptation of root hair cells in plants

- Large surface area to absorb nutrients and water

- Thin walls that do not restrict water absorption.

Adaptation of xylem cells in plants

- No upper or lower margins between cells provide a continuous route for water to flow

- Thick, woody side walls strengthen their structure and prevent collapse.

Adaptation of phloem cells in plants

- Sieve plates let dissolved amino acids and sugars be transported up and down the stem

- Companion cells provide energy needed for active transport of substances along the phloem.

Cell differentiation

The process by which cells become specialised.

Importance of cell differentiation

Allows production of different tissues and organs that perform various vital functions in the human body.

Purpose of cell division in mature animals

Repair and replacement of cells.

Magnification

The number of times bigger an image appears compared to the size of the real object.

Resolution

The smallest distance between two objects that can be distinguished.

Advantages of light microscopes

Inexpensive, Easy to use, Portable, Observe both dead and living specimens.

Disadvantage of light microscopes

Limited resolution.

Advantage of electron microscopes

Greater magnification and resolution.

How electron microscopes have enabled scientists to understand cells

Allow small sub-cellular structures (e.g. mitochondria, ribosomes) to be observed in detail. Enable scientists to develop more accurate explanations about how cell structure relates to function.

Disadvantages of electron microscopes

Expensive, Large so less portable, Require training to use, Only dead specimens can be observed.

How magnification can be calculated

magnification = size of image / size of real object.

How bacteria multiply

Binary fission (simple cell division).

How often bacteria multiply

Once every 20 minutes if enough nutrients are available and the temperature is suitable.

Ways to grow bacteria

Nutrient broth solution, Colonies on an agar gel plate.

Nutrients in nutrient broth solution

All nutrients required for bacteria to grow including nitrogen for protein synthesis, carbohydrates for energy and other minerals.

Preparation of an uncontaminated culture using aseptic technique

1. Use pre-sterilised plastic Petri dishes or sterilise glass Petri dishes and agar gel before using with an autoclave.

2. Pour the sterile agar gel into the Petri dish and allow time to set.

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

4. Dip the inoculating loop into the solution of microorganisms and make streaks with the loop on the surface of the agar.

5. Put the lid on the Petri dish and secure it with tape. Label accordingly then turn and store upside down.

6. Incubate the culture at 25oC in school laboratories.

Sterilisation of Petri dishes, culture media and innoculating loops

To kill any bacteria already present.

Securing Petri dish lid with tape

Stops bacteria in the air contaminating the culture. The lid is not fully sealed to prevent the growth of anaerobic bacteria in a lack of oxygen. Upside down to prevent condensation from forming and dripping down onto the colonies.

Incubation temperature for cultures

Cultures are incubated at 25oC in school laboratories because harmful pathogens are less likely to grow at this temperature.

Formula for cross-sectional area of a bacterial colony

πr² = 3.14, where r = radius (diameter/2).

Calculating number of bacteria from mean division time

1. Calculate the number of times the bacteria will divide in the given time period from the mean division time.

2. Use the following equation: Number of bacteria in population at end of time period = number of bacteria at the beginning of the time period x 2^(number of divisions in the time period).

Chromosomes

Chromosomes consist of DNA molecules combined with proteins. They contain genes which provide the instructions for protein synthesis.

Gene

A section of DNA which codes for a protein.

Chromosomes in human body cells

46

Chromosomes in gametes

23

Arrangement of chromosomes in body cells

Arranged in pairs - 46 chromosomes form 23 pairs.

Stages of the cell cycle

1. Replication of DNA and synthesis of organelles 2. Mitosis 3. Division of cell

Importance of mitosis

Produces identical cells which all have the same genetic information. Produces additional cells for growth and repair.

First stage of the cell cycle

Longest stage - cells grow and increase in mass, replicate DNA and synthesise more organelles (eg. mitochondria, ribosomes).

Second stage of the cell cycle

Each chromosome in a pair is pulled to opposite poles of the cell, then the nucleus divides.

Third stage of the cell cycle

The cytoplasm and cell membrane divide - two identical daughter cells are produced.

Stem cell

An unspecialised cell which is capable of differentiating into other cell types and of self-renewal.

Function of stem cells in embryos

Embryonic stem cells can replicate themselves and differentiate into many other types of cells. Embryonic stem cells may be able to treat conditions such as paralysis and diabetes by dividing to replace damaged cells.

Function of stem cells in adult bone marrow

Adult stem cells can differentiate into several cell types to replace dead or damaged tissues. For example, bone marrow stem cells can form many different types of blood cell.

Function of stem cells in plant meristems

Meristem stem cells retain the ability to differentiate into any type of plant cell throughout their lifespan - they can differentiate into any cell which is required by the plant.

Therapeutic cloning

A cloning method where an embryo is produced with the same genetic makeup as the patient. The stem cells which originate from the embryo will not be rejected by the patient's immune system, so can be used to treat certain medical conditions.

Advantages of cloning plants using meristem stem cells

●Can prevent rare plants from becoming extinct. ●Can produce large numbers of plants with a favourable characteristic. ●Can produce identical plants for research.

Issues associated with embryonic stem cells

●Many embryonic stem cells are sourced from aborted embryos - some people have an ethical/religious objection. ●Development of stem cell therapies is slow, expensive and difficult. ●Adult stem cells infected with viruses could transfer infections to patients. ●If donor stem cells do not have a similar genetic makeup to the patient, an immune response could be triggered.

Diffusion

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

Factors affecting diffusion rate

●Concentration gradient - larger gradient, faster diffusion. ●Temperature - higher temperature, faster diffusion. ●Surface area - larger surface area, faster diffusion.

Examples of diffusion in lungs and kidney

●Lungs: oxygen diffuses into the blood from the lungs and carbon dioxide diffuses into the lungs from the blood, both down their concentration gradient. ●Kidney: urea diffuses from cells into blood plasma so it can be excreted in urine.

Adaptation of single-celled organisms for diffusion

They have a large surface area to volume ratio - maximises the rate of diffusion of molecules to meet the organism's needs.

Surface area to volume ratio calculation

Surface Area = Number of Sides x (Side Length x Side Width) Volume = Length x Width x Depth Ratio = Surface Area:Volume

Factors increasing gas exchange surface effectiveness

●Large surface area ●Thin membrane (short diffusion path) ●Efficient blood supply (animals) ●Ventilation (animals)

Osmosis

The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane.

Isotonic solution to a cell

The concentrations of the external and internal (inside cell) solutions are the same.

Hypertonic solution to a cell

The concentration of the external solution is higher than that of the internal solution (inside cell).

Hypotonic solution to a cell

The concentration of the external solution is lower than that of internal solution (inside cell).

Effect of hypotonic solution on animal cell

Water moves into the cell, causing it to burst.

Effect of hypertonic solution on animal cell

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

Turgor pressure in plants

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

Effect of hypertonic solution on plant cell

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.

Active transport

The movement of molecules from a more dilute solution to a more concentrated solution against a concentration gradient, using energy from respiration.

Active transport in plant root hair cells

Root hair cells use active transport to take up mineral ions from a more dilute solution in soils. Ions such as magnesium and nitrates are required for healthy growth.

Active transport in digestion

Active transport is used to transport glucose from a lower concentration in the gut to a higher concentration in the blood. Glucose is then transported to the tissues where it can be used in respiration.