AQA A - Level Biology Topic 2

Tissue

Tissue

a group of specialised cells

Organ

made of different tissues

Organ system

different organs working together

What is an Animal Cell made of?

1. Organelles (nucleus, endoplasmic reticulum, golgi body, lysosomes, mitochondria, ribosomes) - all have membrane except the ribosomes
2. Cytoplasm (site of chemical reaction)
3. Cell Membrane (holds cell contents together, controls what enters/leaves cell, cell signalling)

Structure of Nucleus?

• contains DNA (made of genes, genes code for making proteins)
• DNA wrapped around histones to form Chromatin
• nucleus has a double membrane, called Nuclear Envelope, which contains pores
• at centre of nucleus is Nucleolus - produces mRNA (copy of a gene)
• rest of nucleus made of Nucleoplasm (contains the DNA/chromatin)

Rough Endoplasmic Reticulum:

has ribosomes on it, makes proteins

Smooth Endoplasmic Reticulum

has no ribosomes on it, makes lipids/carbohydrates

Golgi body?

• modifies and packages proteins
• packages them into vesicles for transport
• digestive enzymes are placed into lysosomes (vesicles with membranes around them)

Mitochondria?

• site of respiration, releases energy, produces ATP (energy carrier molecule)
• has a double membrane, inner membrane folded into Cristae (increases surface area for enzymes of respiration)
• middle portion called Matrix

Ribosomes?

• attached to RER
• site of protein synthesis

What is a Plant Cell made of?

1. Organelles (nucleus, endoplasmic reticulum, golgi body, lysosomes, mitochondria, chloroplast, vacuole, ribosomes) - all have membrane except the ribosomes
2. Cytoplasm (site of chemical reaction)
3. Cell Membrane (holds cell contents together, controls what enters/leaves cell, cell signalling)
4. Cell Wall (made of cellulose, prevents cell from bursting or shrinking)

Structure of chloroplast?

• organelle for photosynthesis
• has double membrane
• contains discs called thylakoids
• thylakoids contain chlorophyll
• stack of thylakoids called granum
• thylakoids surrounded by a fluid called stroma

Vacuole?

Surrounded by a membrane called a tonoplast, contains Cell Sap (water, sugar, minerals)

What is Bacteria made of?

1. No nucleus - loose DNA in the form of a single loop and plasmid
2. No membrane bound organelles: smaller ribosomes, mesosomes - infolding of cell membrane for respiration
3. Cytoplasm
4. Cell Membrane & Cell Wall (made of peptidoglycan/murein)
5. some have a Capsule (reduce water loss, protect from phagocytosis) and Flagella (movement)

What is Virus made of?

1. DNA or RNA (if RNA, also has a enzyme called reverse transcriptase to turn RNA into DNA)
2. Protein Coat called Capsid and Lipid Coat
3. Attachment proteins on outside
4. (infects host cells by attaching using their attachment protein, send in their DNA which uses the cell to make the viruses components and uses the cell membrane to make the viruses lipid coat, hence, producing copies of the virus and destroying the host cell)

Stages of Virus Replication

Attachment, entry, uncoating, viral gene transcription, viral protein translation, assembly, budding off/release

What is a Chromosome?

• DNA in coiled form
• formed during interphase of cell division (mitosis/meiosis) in Animals/Plants
• made of 2 identical/sister chromatids joined by a centromere
• carries 2 copies of the same DNA molecule

What is a homologous pair of chromosomes?

a pair of chromosomes: 1 maternal (from mother)/1 paternal (from father)
carries same genes but different alleles - there are 23 pairs in humans

What is Cell Division?

• formation of new cells in multicellular organisms (animals & plants)
• 2 methods = mitosis & meiosis
• mitosis = produces genetically identical cells for growth & repair of tissues
• meiosis = produces genetically different haploid cells as gametes for sexual reproduction

What does Mitosis (cell cycle) produce?

2 genetically identical cells, diploid (have full set of chromosomes/DNA)

Benefit of Mitosis?: growth and repair of tissues

Stages of Mitosis?: Interphase/Mitosis/Cytokinesis

Interphase?: G1- protein synthesis
S- DNA replication (doubles set of DNA)
G2- organelle synthesis

Mitosis?

part of eukaryotic cell division during which the cell nucleus divides

PMAT?

prophase, metaphase, anaphase, telophase

1. Prophase -DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form
2. Metaphase- chromosomes line up in middle of cell and attach to spindle fibre via centromere
3. Anaphase- spindle fibres pull, centromere splits, sister chromatids move to opposite sides
4. Telophase- chromatids uncoil, nucleus reforms (left with 2 genetically identical nuclei)

Cytokinesis?

separating cell into 2 (each receives a nucleus and organelles/cytoplasm)

What happens to DNA mass in mitosis?

halves

What happens to Chromosome number in mitosis?

stays the same (diploid)

What is Cancer?

formation of a tumour due to uncontrolled cell division (uncontrolled mitosis)

How does uncontrolled cell division occur?

1. due to mutation of DNA/cells forming cancer cells
2. mutation can occur randomly or due to mutagens (chemicals/radiation)
3. cancer cells are rapidly dividing cells (like hair cells, skin cells, red blood cells), they spend less time in interphase and more time in the other stages (mitosis)

Treatment for Cancer?

1. Surgery = aim is to remove tumour

2. Chemotherapy = - using drugs that inhibit mitosis in rapidly dividing cancer cells
- problem, also affect normal healthy cells (hair cell, skin cells, rbcs) causing side effects (hair loss, dry skin, tiredness)
- treatment given as regular doses to allow time for normal healthy cells to recover in number

3. Radiotherapy = radiation used to destroy cancer cells

How do Bacteria do Cell Division?

Binary Fission
Copy their DNA (Single Loop and Plasmids) and then separate into 2 new genetically identical bacteria [Asexual Reproduction]

2 types of microscopes?

Light and Electron (transmission and scanning)

How to judge a microscope?

by Magnification and Resolution

Magnification?

how much larger the image size is compared to the actual size

Formula for magnification?

magnification = image size/actual size

Conversion?

1 mm = 1000 micrometre. 1 mm = 1,000,000 nanometre

Why can organelles appear different in images?

viewed from different angles and at different levels/depth

Resolution?

minimum distance at which 2 very close objects can be distinguished

Why does electron microscopes have a higher resolution?

Electron microscope uses electrons which have a shorter wavelength (light microscope uses light which has a large wavelength)

Difference between TEM and SEM?

in Transmission the electrons pass through the specimen, in Scanning the electrons bounce off the specimen's surface

Advantage and Disadvantage of TEM?

• Advantage = highest magnification and highest resolution
• Disadvantage = works in a vacuum so can only observe dead specimens, specimen needs to be thin, black and white image, 2D image, artefacts

Advantage and Disadvantage of SEM?

• Advantage = produces 3D image
• Disadvantage = works in a vacuum so can only observe dead specimens, black and white image, artefacts

Cell Fractionation?

Breakdown tissue into cells (cut, pestle & mortar)

Simple diffusion

molecules move directly through the phospholipid bilayer

Facilitated diffusion

molecules pass through transport proteins (large use carrier, charged use channel)

Factors that affect rate of diffusion?

1. surface area (increase = increase rate of diffusion)
2. concentration gradient (increase = increase rate of diffusion)
3. thickness (decrease = decrease diffusion distance = increase rate of diffusion)
4. temperature (increase = increase kinetic energy = molecules move faster = increase rate of diffusion)
5. size of molecules (smaller molecules = increase rate of diffusion)

What is Ficks Law?

(Surface Area x Concentration Gradient)/Thickness

Osmosis

movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane

Active Transport

movement of molecules from an area of low concentration to an area of high concentration using ATP and carrier proteins (against concentration gradient)

process of active transport

1. molecules (in area of low concentration) bind to carrier protein
2. ATP breaksdown to ADP, Pi and Energy
3. the Pi and Energy cause the carrier protein to change shape
4. carrier protein releases molecules on opposite side (in area of high concentration)
5. the carrier protein releases the attached Pi to return to its original shape

What is a pathogen?

• a disease causing micro-organism e.g. bacteria, virus, fungi
• bacteria cause disease by producing toxins
• virus cause disease by dividing in cells causing them to burst

Non Specific Barriers against pathogens?

prevents pathogens entering the body

Phagocytes

perform phagocytosis (non specific) and stimulate specific response

Specific Response

uses B and T lymphocytes to produce memory cells and antibodies

What are the Non-specific Barriers?

1. Skin, an impermeable barrier made of keratin
2. Cilia & Mucus in Lungs
3. Stomach Acid (denatures/breaks down pathogens)

Describe the process of Phagocytosis ?:

1. pathogen releases chemicals
2. this attracts the phagocyte
3. the phagocyte binds to the pathogen
4. the phagocyte engulfs the pathogen
5. forms a phagosome around the pathogen
6. lysosomes inside the phagocyte release digestive enzymes (lysozymes) into the phagosome
7. breaking down the pathogen by hydrolysis

Describe the Specific Response?

1. Phagocytes perform phagocytosis (engulf and destroy pathogen) without destroying the antigen.
2. t lymphocytes (t cells) bind to the antigen and become stimulated
3. they divide by mitosis to form 3 types of cells: t helper, t killer, t memory
4. t helper cells stimulate b lymphocytes (b cells)
5. t killer cells kill infected cells (infected by virus)
6. t memory cells provide long term immunity
7. the b cells become stimulated and divide by mitosis to make 2 types of cells: Plasma Cells & B Memory Cells
a) Plasma cells make antibodies which engulf antigen
b) B memory cells provide long term immunity

What is a antigen?

a protein on the surface of a pathogen that stimulates an immune response

How does the immune response lead to production of antibodies?

the phagocytes stimulate the t cells, the t cells form t helper cells, the t helper cells stimulate the b cells, the b cells form plasma cells, the plasma cells make antibodies

What is an antibody?

1. a globular protein
2. made by plasma cells
3. has 3 regions: variable region, hinge region, constant region
4. variable region has a different shape in each antibody, contains the antigen binding sites, these bind to complementary antigens (on a pathogen) to form an antigen-antibody complex, destroying the pathogen
5. hinge region gives the antibody flexibility
6. constant region the same shape in all antibodies, binds to phagocytes to help with phagocytosis

How do Memory cells (B/T) work?

1. They are made during the specific immune response after a new infection by a pathogen (called a primary infection)
2. B and T memory cells remain in the blood
3. if person is reinfected by the same pathogen (called a secondary infection) the memory cells will recognise the pathogen and produce antibodies RAPIDLY and to a LARGE amount
4. therefore the pathogen is killed before it can cause harm = immunity

How does a vaccine produce immunity?

involves giving an injection that contains dead/weakened pathogens that carry antigens which stimulates the immune response leading to production of antibodies & memory cells

Active immunity?

individual has memory cells - can make their own antibodies & provides long term immunity

Passive immunity?

person given antibodies, these work then die, no long term immunity, no memory cells.

How does active immunity occur?

naturally = by primary infection, artificially = by vaccination

How does passive immunity occur?

naturally = from mother to baby (placenta or breast milk), artificially = by injection

Successful Vaccination Programme?

produce suitable vaccine (effective - make memory cells, does not cause disease, no major side effects, low cost, easily produced/transported/stored/administered)
herd immunity

What is herd immunity?

when a large proportion of the population is vaccinated, therefore most people will be immune, only a few will not be a immune, increases chance of non-immune person coming into contact with immune person, so the pathogen has no where to go, so it dies out

Problems with Vaccination Programmes?

• vaccine does not work (dead form ineffective, pathogen hides from immune system)
• vaccine not safe (no weak/inactive form, causes major side effects)
• many strains of pathogen
• cannot achieve herd immunity (logistic of vaccinating large proportion)
• antigenic variability

What is antigenic variability?

the pathogen mutates, the antigen changes shape, so the memory cells no longer complementary - do not recognise the pathogen, therefore the pathogen can reharm

HIV, Human Immunodeficiency Virus

the Pathogen, spread by fluid to fluid contact (unprotected sexual intercourse, sharing needles, mother to child via placenta or breast feeding)

What does HIV do?

damages and destroys T Helper Cells, therefore person no longer produces Immune Response and has no defence to against pathogens/infections = AIDs

AIDs, Acquired Immunodeficiency Syndrome

Infectious disease caused by HIV

What does AIDS do?

puts individual at risk from all sorts of pathogens/infections