IB Biology SL Review Flashcards

Vocabulary flashcards for key concepts in IB Biology SL, based on lecture notes.

Transpiration

The movement of water through a plant, and its evaporation from aerial parts of the plant such as leaves.

Transpiration Process (6)

1. Water evaporates from the mesophyll cells, and diffuses out through the stomata.

2. Water is drawn out of the xylem, moving through cell walls, by capillary action, to replace water lost by mesophyll cells.

3. The loss of water in the xylem creates a negative pressure in the leaf.

4. Water enters the root by osmosis and moves into the xylem in the roots, creating higher pressure.

5. Water is cohesive, allowing it to move up the xylem from the roots to the leaves by transpiration pull.

6. The adhesive properties of water will enable it to form hydrogen bonds with the cellulose in the cell wall, helping to maintain the movement of water up the xylem.

Photosynthesis

The transformation of light energy into chemical energy in the form of carbon compounds in the chloroplast. Glucose is used to synthesise macromolecules of life.

Chlorophyll

A green light-absorbing pigment found in leaves that is contained within chloroplasts. They absorb blue and red light best and reflect green light.

Photolysis

Part of the light-dependent reactions whose role is to generate energy in the form of ATP using electrons from the splitting of water. This requires light and occurs in the thylakoids of chloroplasts.

The energy in photons is used to split water molecules into hydrogen ions and oxygen gas. Hydrogen ions are used with carbon dioxide to produce glucose. Oxygen released as a waste product. Glucose produced → to produce other organic compounds.

Active Transport

The movement of particles from a region of low concentration to a region of high concentration using protein pumps and ATP energy.

Active Transport Process (5)

1. A specific particle binds to a binding site on a particular protein pump.

2. ATP binds to the protein pump and hydrolyzes to become ADP.

3. A phosphate remains attached to the protein pump and causes the protein pump to change shape.

4. The particle is moved against the concentration gradient and released.

5. The phosphate is released, causing the protein pump to return to its original shape.

Transcription

The synthesis of RNA, using DNA as a template. RNA polymerase is used. Occurs in a 5’ to 3’ direction.

Transcription: Initiation

RNA polymerase binds to the DNA at the start of the gene. It then separates the two strands of DNA by breaking hydrogen bonds, exposing the bases

Transcription: Elongation

1. Happens at the start of the gene.

2. RNA polymerase builds a molecule of mRNA on one of the DNA strands by condensation reactions.

3. The strand used is called the template strand and the other strand is called the coding strand.

4. RNA polymerase moves along the DNA.

5. Free RNA molecules are added to the growing mRNA

Transcription: Termination

A terminator sequence in the DNA is reached and mRNA is released. RNA polymerase detaches from the DNA strand, allowing the 2 strands to come together again.

Translation

The synthesis of polypeptides by ribosomes. Ribosomes require messenger RNA (mRNA) and transfer RNA (tRNA) to synthesise polypeptides. mRNA brings the genetic code to the ribosome, and tRNA brings amino acids to the ribosome.

Translation Process (9)

1. Specific codons for each amino acid

2. The small ribosomal unit binds to mRNA at the start codon

3. A tRNA with a complementary anticodon binds to the mRNA codon by hydrogen bonding

4. A large ribosomal subunit attaches to form a ribosome

5. A 2nd tRNA molecule enters, as there are 2 tRNA binding sites in the large ribosomal subunit

6. Peptide bond forms between 2 amino acids by condensation reaction, releasing one tRNA from the ribosome

7. The ribosome moves from codon-codon along the mRNA, adding an amino acid to a growing polypeptide

8. When the ribosome reaches a stop codon, the large and small subunits separate

9. tRNA and polypeptide are released

Movement of Ribosomes in Translation

The ribosomes move along mRNA from codon to codon. At each codon, tRNA enters the ribosome. When 2 tRNAs are present in the ribosome, a peptide bond forms between amino acids. One tRNA loses amino acid and leaves the ribosome. Polypeptide chain grows as the ribosome moves from codon to codon. The polypeptide, small and large subunits and tRNA released when the stop codon enters the ribosome.

Polymerase Chain Reaction (PCR)

A method for amplifying (making many copies of) a DNA sequence from a small sample, using cycles of heating and cooling to amplify a sample of DNA.

Taq DNA Polymerase

A heat-stable DNA polymerase used in PCR, obtained from a bacterium adapted to living in hot springs.

PCR Process (4)

1. Denaturation: The DNA sample is heated to 95°C to break hydrogen bonds and separate the two DNA strands.

2. Annealing: Temperature is reduced to 54°C which allows DNA primers to bind to both strands of DNA, next to the sequence to be copied.

3. The temperature is increased to 72°C which allows Taq DNA polymerase to replicate both strands, starting at the primer. This produces two identical double-stranded DNA molecules. Both of these are exact copies of the original DNA molecule.

4. Steps #1 - #3 are repeated many times to produce many copies of the DNA.

Gel Electrophoresis

A technique used to separate charged molecules like DNA or proteins.

DNA Profiles

A pattern created from an individual's DNA fragments, using gel electrophoresis; unique; and used in forensic science and paternity testing

Restriction Endonuclease

An enzyme that cuts DNA into many negatively charged fragments for gel electrophoresis.

Gel Electrophoresis Process (9)

1. DNA is an acid and dissociates to become negatively charged in water.

2. Restriction endonuclease enzymes cut DNA into many negatively charged fragments.

3. The DNA fragments move from the negative electrode to the positive electrode in an electrophoresis chamber.

4. A sample of DNA is obtained and amplified using PCR.

5. DNA samples are cut into fragments using restriction endonucleases.

6. The DNA is inserted into wells in agar gel which is in a salt solution.

7. Electricity is run through the salt solution.

8. The (negatively charged) DNA fragments move towards the positive electrode. Small (lighter) fragments move faster than bigger (heavier) fragments.

9. When a dye is added, a pattern becomes visible. The pattern is the DNA profile.

Neurons are at resting potential (-70mV)

Neurons are at resting potential (-70mV) when a nerve impulse is not being transmitted. The potential difference is maintained by sodium ions being outside the axon of a neuron, and potassium ions and chlorine ions being inside the axon.

Sodium-Potassium Pump (SPP)

A pump involved in transporting Na+ out of the axon and K+ into the axon against their concentration gradients. — Active Transport

Action of SPP (7)

1. 3 Na+ attaches to the sodium ion binding sites on the SPP protein

2. ATP attaches to SPP

3. ATP is hydrolysed, with phosphate remaining attached to the protein pump. ADP is released.

4. Phosphate causes the pump to change shape, moving sodium across the axon membrane, and releasing Na+ outside the axon

5. 2 K+ attach to potassium ion binding sites on SPP protein

6. Phosphate is released from the pump

7. The pump returns to its original shape moving the K+ into the axon

Blood Clotting

Prevents the loss of blood and the entry of pathogens.

Blood Clotting Process (5)

1. Damaged tissue and platelets release clotting factors which initiate a cascade of reactions to form a blood clot.

2. Clotting factors convert inactive prothrombin to (active) thrombin

3. Thrombin is an enzyme that converts soluble fibrinogen to insoluble fibrin

4. Fibrin forms a mesh around wounds, trapping blood cells to form a semi-solid clot

5. Clot dries to form a scab, preventing blood loss and entry of pathogens

Antibodies

Lymphocyte B-cells produce these and memory cells after being activated by contact with helper T-cells and a specific antigen.

Process in Producing Antibodies

1. A pathogen enters the body and is engulfed by a phagocyte.

2. The antigen is attached to an MHC protein.

3. Phagocytes present the antigen by moving it onto the plasma membrane using MHC protein.

4. Helper T-cells have specific receptor proteins in their plasma membrane that recognize and bind to antigens presented by phagocytes.

5. The phagocyte passes a chemical signal to the helper T-lymphocyte to activate the T-lymphocyte.

6. Inactive B-lymphocytes have (specific) antibodies on their plasma membranes.

7. Binds if the antigens on Helper T-lymphocytes match antibodies present on B-lymphocytes.

8. The B-lymphocyte is activated by this interaction.

Condensation of Chromosomes

The process where Chromatin condenses to form visible chromosomes, with sister chromatids, during the prophase of mitosis and prophases I and II of meiosis. During condensation, DNA coils around histone proteins to form nucleosomes. The nucleosomes coil around each other to form chromosomes with sister chromatids.

Interphase

Longest phase of the cell cycle, where the cell grows, replicates its DNA and prepares for mitosis.

Prophase (Mitosis)

Chromatin condenses to form chromosomes (2 identical sister chromatids attached to a centromere); membrane breaks down; centriole moves towards the poles producing spindle fibres; chromosomes attach to spindle fibres at the centromere.

Metaphase (Mitosis)

Chromosomes line up along the equator of the cell, attached to spindle fibres.

Anaphase (Mitosis)

Spindle fibres separate sister chromatids at the centromere to form single-stranded chromosomes; microtubule motors move chromosomes to opposite poles of the cell.

Telophase (Mitosis)

Chromosomes arrive at opposite poles, forming nuclear membranes around them; chromosomes uncoil to form chromatin and 2 genetically identical nuclei are produced; cytokinesis begins during telophase to produce a genetically identical daughter.

Meiosis

A nuclear division which produces haploid cells, involving two nuclear divisions; a reduction division which produces four haploid nuclei.

Meiosis I segregates the homologous chromosomes to produce two haploid cells.

Meiosis II segregates the sister chromatids producing four haploid cells.

Prophase I (Meiosis)

Homologous chromosomes pair up to form bivalents; crossing over occurs when alleles switch between non-sister chromatids; chromatin condenses to form sister chromatids; centrioles move towards the poles and produce spindle fibres; nuclear membrane breaks down.

Metaphase I (Meiosis)

Spindle fibres move bivalents to the equator; sister chromatids are attached to spindle fibres; maternal and paternal homologous chromosomes are randomly assorted as they line up along the equator of the cell.

Anaphase I (Meiosis)

Homologous chromosomes are separated and pulled towards the poles of the cell by the spindle fibres; microtubule motors move chromosomes to opposite poles of the cell.

Telophase I (Meiosis)

Chromosomes (sister chromatids) arrive at the poles and uncoil; nuclear membrane forms around sister chromatids to produce 2 haploid nuclei; cytokinesis occurs to produce 2 haploid cells.

Prophase II (Meiosis)

Chromosomes (sister chromatids) supercoil and appear in both haploid cells; centrioles move towards the poles producing spindle fibres; sister chromatids attach to spindle fibres at the centromere.

Metaphase II (Meiosis)

Chromosomes with sister chromatids line up along the equator, attached to spindle fibres; single chromosomes line up at the equator (not bivalents like in metaphase I).

Anaphase II (Meiosis)

Sister chromatids are pulled apart producing single-stranded chromosomes which are moved towards the poles by microtubule motors.

Telophase II (Meiosis)

Chromosomes reach the poles of each cell and uncoil; nuclear membrane forms around each cell; cytokinesis occurs in both cells, forming 4 cells with haploid nuclei which are not identical.

Ventilation

The movement of air in and out of the alveoli in the lungs, facilitating gas exchange. Maintains concentration gradients of oxygen and carbon dioxide between the air in alveoli and blood flowing in adjacent capillaries.

Inspiration

The diaphragm contracts and moves downwards. The external intercostal muscles contract, moving the ribcage up and out. The volume in the thorax increases, decreasing the pressure in the lungs. Air passively moves from the surrounding air (with high pressure) into the lungs with low pressure.

Expiration

The abdominal muscles contract and push the diaphragm upwards. The external intercostal muscles relax and the internal intercostal muscles contract, moving the ribcage down and inwards. The volume in the thorax decreases, increasing the pressure in the lungs. The high pressure in the lungs moves air out of the lungs to the surrounding air, where pressure is lower.

The Menstrual Cycle

1. Falling oestradiol and progesterone levels stimulate the pituitary gland to produce FSH. The endometrium breaks down.

2. Rising FSH levels cause follicles to develop.

3. The developing follicles secrete oestradiol.

4. The rise in oestradiol levels stimulates the repair of the endometrium.

5. Oestradiol reaches a peak, which stimulates the pituitary gland to secrete LH.

6. LH quickly rises to a peak, causing the egg to be released from the dominant follicle. This is ovulation.

7. The rise in LH causes less oestradiol to be secreted (Negative feedback)

8. The remains of the follicle are now called the corpus luteum.

9. The corpus luteum secretes large quantities of progesterone, which causes the endometrium to prepare for pregnancy.

10. High levels of progesterone inhibit the production of FSH and LH.

11. The corpus luteum breaks down if the egg is not fertilised, resulting in falling levels of progesterone.

12. The cycle begins again as FSH levels increase due to falling levels of progesterone.

Positive Feedback in Menstrual Cycle

FSH and Oestrogen

LH and Oestrogen

Negative Feedback in Menstrual Cycle

LH and Progesterone

IVF Process (10)

1. The normal menstrual cycle is halted using oestradiol.

2. High doses of FSH are injected into the female to stimulate follicle development. This is known as superovulation as up to 20 eggs can develop.

3. The hormone human chorionic gonadotropin (hCG) is injected into the female, which stimulates the eggs to mature.

4. The eggs are harvested.

5. Sperm are collected from the male. They may be screened to ensure that they are healthy.

6. The eggs are mixed with up to 100,000 sperm to allow fertilisation, and incubated (at 37°C). OR a single sperm is micro-injected directly into the egg.

7. The fertilised egg is now a zygote which divides by mitosis to produce an embryo.

8. One or more embryos are placed in the woman’s uterus after 48 hours (again, screening is possible)

9. Extra progesterone is provided (a tablet inserted in the vagina), to maintain the endometrium.

10. The pregnancy continues as a normal pregnancy.

Baroreceptors

Stretch-sensitive receptors that monitor blood pressure

Chemoreceptors

Detects changes to blood chemistry (CO2, O2 and pH) and help regulate ventilation rate

Feedback control of heart rate

Exercise increases rate of respiration which increases carbon dioxide levels, resulting in a decrease in blood pH levels due to the production of carbonic acid. Chemoreceptors in aorta and carotid artery montior changes, senidng signals to cardiovascular control centre of medulla oblongata (MO). MO sends signals to sinoatrial node to increase heart rate.

Feedback Control of Ventilation Rate

CO2 in the blood decreases the blood pH. Chemoreceptors in the carotid artery and the MO monitor changes in the pH of the blood.

Exercise increases the respiration rate of muscles, releasing more CO2 in the blood. Higher levels of CO2 in the blood reduce the pH of the blood because CO2 forms carbonic acid. Chemoreceptors in the medulla oblongata monitor the decrease in blood pH. The respiratory control centre of the medulla oblongata sends nerve impulses to the intercostal muscles and diaphragm, increasing the rate and depth of ventilation. Vice versa for after exercise.

Thermoregulation

When an organism maintains its body temperature within a narrow range; it involves negative feedback loops to maintain body temperature.

Thermoregulation Process

1. Peripheral thermoreceptors monitor body temperature. When peripheral thermoreceptors sense a change in body temperature, they send nerve signals to the thermoregulatory centre of the hypothalamus in the brain.

2. The hypothalamus monitors body temperature and initiates a range of negative feedback responses to warm up or cool down the body as required.

3. The hypothalamus sends nerve signals to the skeletal muscles when body temperature drops, which results in shivering. The muscles are examples of effectors (they are stimulated by motor neurons).

4. The pituitary gland secretes thyroid stimulating hormone which regulates the secretion of thyroxine from the thyroid gland, which is involved in the control of metabolic rate in cells of the body. An increase in thyroxine levels leads to an increase in the rate of metabolism. Metabolism generates heat to warm up the body.

5. Adipose tissue (body fat) is found under the skin, and acts as an insulator, reducing heat loss.

Cell Specialisation

• Fertilisation is the fusion of gametes which leads to the development of a zygote, which is a totipotent stem cell.

• Totipotent stem cells can develop into all other cell types or develop into an embryo.

• The zygote develops into a blastocyst through cell division over 5 days. The blastocyst contains pluripotent embryonic stem cells, which means that they can differentiate into all other cell types but not into an embryo.

• The blastocyst develops into a foetus, as the embryonic stem cells differentiate into specialised stem cells.

• Some adult stem cells remain to replenish dying cells and repair damaged tissues.

• Most adult stem cells are multipotent meaning that they can form into a range of closely related cells.

• Hematopoietic stem cells are also multipotent and can develop into all types of blood cells, but not other cell types.