2.75

2.75 Recall that urine contains water, urea and salts

Urine contains water, urea and salts. Salt and water affect the concentration of tissue fluid (osmoregulation). The removal of urea is part of the excretion of metabolic waste. Concentration of urine depends on the condition of the body. 

2.74

2.74 Describe the role of ADH in regulating water content of the blood

The amount of water in your urine is controlled by a hormone called antidiuretic hormone (ADH); this is made by a gland in hypothalamus. It flows through the bloodstream and targets the kidney (collecting duct). ADH allows more water to come out of the collecting duct by making the walls more porous. The effect is to control and alter the composition or quantity of water in blood. ADH has the ability to make the blood more or less concentrated (tissue fluids must be isotonic with the cytoplasm of the cell).

Collecting duct is responsible for selective reabsorption of water and this is affected by the amount of ADH in the blood. The consequence of ADH secretion is more concentrated urine and lower volume.

When it is hot, more water would be lost as sweat so more ADH would be produced. When it is cold, less water would be lost so less ADH would be produced. When one is dehydrated, they want to keep the water in the body so more ADH would be produced. 


ADH makes the collecting duct more porous allowing more water to be reabsorbed into the bloodstream. 

2.73

2.73 Understand that selective reabsorption of glucose occurs at the proximal convoluted tubule

In PCT, glucose is removed and taken back into the blood. Glucose is selectively reabsorbed into the blood in the proximal convoluted tubule. Urine does not contain glucose. If glucose is in urine, this is an indication of diabetes.

2.72

2.72 Understand that water is reabsorbed into the blood from the collecting duct

During ultrafiltration, too much water is filtered. So the filtrate passes through the PCT to loop of Henle. When it reaches the collecting duct, water is removed from the filtrate. Water returned back to the blood vessels. Water has been selected and reabsorbed. Selected reabsorption of water occurs in the collecting duct. 

2.71

2.71 Describe ultrafiltration in the Bowman’s capsule and the composition of the glomerular filtrate

The nephrons filter blood and remove waste from the body. Waste consists of urine, which is largely water, salts and urea. At the beginning of the nephron (Bowman’s capsule), ultrafiltration begins. Blood arrives in the kidney in afferent arteriole (high pressure), which branches into blood vessels of the glomerulus. The blood vessel exiting is smaller in diameter, which means it has a high blood pressure. This forces the plasma and all the dissolved components (water, salts, amino acids, glucose and urea) into the Bowman’s capsule. The plasma is now called the glomerula filtrate. All these are filtered into the space inside of the Bowman’s capsule. Only the large plasma proteins remain in the blood and continue to the PCT. 

2.70

2.70 Describe the structure of nephrons, to include Bowman’s capsule and glomerulus, convoluted tubules, loop of Henle and collecting duct

Inside each kidney, there are thousands of tiny tubes called nephrons. They filter your blood and remove waste chemicals. Blood is brought to each kidney in the renal artery, which contains a lot of waste chemicals like urea. The artery branches many times, and each branch ends with a bunch of capillaries called a glomerulus. The glomerulus is inside part of the nephron called the Bowman’s capsule (double-walled, cup-shaped), the first part of the kidney tubule. As blood passes through each glomerulus, that large molecules like blood proteins can’t pass through while small molecules like urea, glucose, salts and water pass out of the glomerulus into the nephrons. This is because the filter is like a net with tiny holes. The leftover urea and waste salts are dissolved in water to produce urine. It flows down the ureter to the bladder. The clean blood leaves the kidney into the renal vein. 

Nephron: functional unit of the kidney that does the filtration and controls the composition of the blood.

Aorta à Renal artery à blood into the kidney à the kidney filters the blood à Urine removed from blood à comes down the ureter à collects in the bladder for release

(Other cleaned blood enters the renal vein into the vena cava.)

The space in the middle is known as the pelvic region (NOT THE SAME AS PELVIS). Urine gets collected in this area and drains down the ureter.

They are labelled in different colours because the kidney is made up of millions of tubular structures.

The tubes are twisted into sections known as proximal (first twist) and distal (second twist) convoluted tubules (aka PCT and DCT).

The arrangement of the tubules gives the different colours in the kidney. There are millions of tubules of nephrons in a kidney.

2.69

2.69 Describe the structure of the urinary system, including the kidneys, ureters, bladder and urethra

The right and the left kidneys, each have separate blood supplies. They carry out excretion, filtration and osmoregulation. There is a tube coming out from each kidney (ureter), which carries urine to the bladder. Urine collected in the bladder is excreted through the urethra, down the vagina/ penis.

2.68 Osmoregulation

Osmoregulation

Osmoregulation is the control of osmosis. The tissue fluid (highlighted in yellow) surrounding the cells must be isotonic with the cytoplasm of the cells. Blood going in and out of the fluid must be equal so that the cells maintain their size. If the blood circulating into the tissue is too concentrated, causing a hypertonic fluid, too much water will be removed from the cells. In this case, the kidneys will remove less water and more salts to maintain the balance. Too diluted fluid will cause a hypotonic fluid, where too little water will be removed from the cells. In this case, the kidneys will have to excrete more water adn less salts. Both are undesirable. We want the cytoplasm to be isotonic.

This can be controlled by the kidney controlling the composition of the blood circulating through the kidneys. Excess water and salts can be removed and excreted down through the ureter. By controlling the content of water and salts in the blood, the kidney can keep the tissue fluid isotonic, maintaining the function of the cells. 

2.68 Excretion

2.68 Understand how the kidney carries out its roles of excretion and of osmoregulation

Excretion

Chemical reactions in your body produce waste like carbon dioxide and urea. Urea contains nitrogen which is toxic and cannot be stored. Originally, urea was amino acids. They are used for growth, but excess amino acids must be removed since they are toxic.

1) Blood circulates to the liver. Amino acids are broken down and converted into urea (process of deamination).

2) Blood re-enters the bloodstream and goes to both of the kidneys. The kidneys will filter the urea from the blood. Water will be added to urea to form urine. Urine will drain down the ureter and will be collected in the bladder.

3) Filtered blood returns to the circulation without urea. 

Amino acids --> LIVER --> Urea --> (less toxic) --> Kidneys

2.67b

2.67 recall that the lungs, kidneys and skin are organs of excretion

Major organs of excretion: lungs, kidneys and skin

1) Lungs: excrete CO₂

2) Kidneys: excrete excess water, urea and salts. This helps the body control the level of water. Urea is the nitrogen waste from amino acids; we can’t store amino acids, so we excrete them as urea.

3) Skin: excretes water & salts (sweating) and a little bit of urea. 

2.67a

2.67 recall the origin of carbon dioxide and oxygen as waste products of metabolism and their loss from the stomata of a leaf

1) Photosynthesis à O₂ excreted

Leaves absorb light energy, combines with CO₂ and water to form glucose and O₂. O₂ gas is the metabolic waste.

2) Respiration à CO₂ excreted

Plants carry out aerobic respiration where glucose and O₂ are combined together. They go through an enzyme reaction and ATP, water and carbon dioxide are formed. CO₂ is the metabolic waste here. (excretion)

3.34

3.34 understand that the incidence of mutations can be increased by exposure to ionising radiation (for example gamma rays, X-rays and ultraviolet rays) and some chemical mutagens (for example chemicals in tobacco).

Causes of mutation: 1) Radiation – Ionising radiation like x-rays and UV rays (à skin cancer)

2) Chemicals – e.g. tars in tobacco à cancerous conditions

Mutagens: chemicals that cause mutations

Carcinogens: chemicals that cause mutations and cancer

3.33

3.33 understand how resistance to antibiotics can increase in bacterial populations

Staphylococcus aureus treated by methicillin (antibiotic)

At first the susceptible form is more common (MSSA), but as the antibiotic is applied, the bacteria that does not die (MRSA) will become more common. The mutation has created genes that break down the antibiotic. As antibiotics are used across time, MRSA increasingly survives and becomes more common. This can be a serious problem in hospitals and treatment. 

3.32

3.32 understand that many mutations are harmful but some are neutral and a few are beneficial

First copy of the gene à mutation à new alleles (responsible for phenotype) à results: beneficial, neutral or harmful. Examples:

Beneficial: improve efficiency of enzyme

Harmful: production of non-functional enzyme

Neutral: at first neutral, may become beneficial or harmful after environmental change

3.31

3.31 describe the process of evolution by means of natural selection

Evolution: 1) Change in the form of organisms (new forms rising)

2) Change in the frequency (how many) of alleles

Natural Selection: is the mechanism of evolution first proposed by Charles Darwin (it is a process)

EXAMPLE:

Staphylococcus aureus causes skin infection and lung infection from wounds (e.g. operation wounds).

Methicillin is an antibiotic that kills MSSA (Methicillin Susceptible Staphylococcus Aureus).

A random mutation occurs à develop of breaking down methicillin à no longer killed by this antibiotic à RESISTANT FORM

Now there are two forms of these bacteria (definition of evolution 1).

When antibiotics are applied, the MRSA (Methicillin Resistant Staphylococcus Aureus) survive and become common à increase in frequency of allele for resistance (definition of evolution 2)

2 features of natural selection (process)

- Random mutation à produces MRSA

- Non-random selection due to the antibiotic à selects MRSA à to survive, MSSA selected and killed

3.30

3.30 recall that mutation is a rare, random change in genetic material that can be inherited

Different alleles exist due to mutation, which changes the base sequence – e.g. ACT à AAT

This creates a new version of the allele à production of an entirely different protein à completely different phenotype

3.29

3.29 understand that variation within a species can be genetic, environmental, or a combination of both

Variation: differences in phenotypes of individuals (in how things appear)

It is possible to count or measure these differences and show them in graphic form

Individual’s phenotype = genotype + environment

V_population = V_genotype + V_environment

1)     Purely affected by the genotype – e.g. blood group

2)     Affected by both the genotype and the environment – genetic variation in genotype + modification by the environment to form a smooth curve – e.g. height in humans

3)     Purely affected by the environment, genes have no role to play and this cannot be inherited – e.g. home language

NUMBER 2: GENOTYPE AND ENVIRONMENT

3.20

3.20 understand how to interpret family pedigrees

Inherited condition: filled in squares / circles (OFTEN diseases not always)

Circles and squares are phenotypes (can be observed)

DOMINANT OR RECESSIVE for those affected

Hypothesis 1: Dominant, caused by DD or Dd

That means the son is DD or Dd, which means at least one of the parents need to have a D, but since the parents are not affected, this cannot be true.

Hypothesis 2: Recessive, caused by dd

If both parents were Dd, then, one d from each of the parents might have been inherited to the son, resulting in dd. TRUE

à This inherited condition is caused by HOMOZYGOUS RECESSIVE GENOTYPE of dd 

3.21

3.21 predict probabilities of outcomes from monohybrid crosses

Chances of outcomes of offspring from monohybrid involving just the one gene

Parents (phenotype): Red x White (monohybrids)

Genotype: RR x rr

Meiosis R, R, r, r (homozygous) à Random fertilisation

Genotype offspring: Rr (all) 100%

(F₁) Phenotype offspring: ALL red

F₁ cross F₁ x F₁

Parent Phenotype: Red x Red

Parent Genotype: R, r, R, r (heterozygous)

Meiosis à Random fertilisation

Genotype offspring: RR: 2Rr: rr

Phenotype ratio (F₂): 3:1 (red:white)

3.19

3.19 describe patterns of monohybrid inheritance using a genetic diagram

Monohybrid: one gene (2 alleles)

P₁ x P₁ Monohybrid cross

Parental phenotypes: red and white (P₁)

Parental genotypes:  GG x gg

Meiosis à production of gametes G G g g 

Random fertilisation: 

F₁ cross F₁ x F₁

Phenotype: Red x Red (F₂)

Genotype: Rr x Rr

Meiosis à Gametes: R r R r

Fertilisation:

Monohybrid F₂ ratio     3:1

Genotypes of the F₂: 1RR: 2Rr: 1rr

Phenotype of the F₂: 3Red: 1White

(PREDICTION STATED BY RATIO: F₂ ratio of 3:1)

3.18

3.18 recall the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and codominance

Phenotype: what we can see, all possible outcomes, red and white petals

Red x Red = Red, White x White = White, Red x White = Red

Dominant: red R

Recessive: white r

Genotype: combination of 2 alleles, the sum total of genes transmitted from parent to offspring

Homozygous: having identical alleles at corresponding chromosomal loci, same alleles RR (red) or rr (white)

Heterozygous: having dissimilar alleles at corresponding chromosomal loci, different alleles Rr (red)

R (dominant) and r (recessive) are alleles.

Codominance: where both parents’ alleles contribute into producing an unusual third phenotype

B – blue petals, genotype BB

W – white petals, genotype WW

B x W = yellow petals, unusual third phenotype BW – CODOMINANCE

B = W both contribute to the phenotype

3.9b

3.9 recall the structure and function of the male and female reproductive systems

Female reproductive organ

Ovary – (a) meiosis occurs here and production of eggs (female gametes)

Oviducts (fallopian tube) – (b) carry eggs to the uterus, location of fertilisation

Uterus – (c) the centre, wall of uterus, made of muscle,

stretch to accommodate pregnancy, contract during birth

Lining of uterus – (g) develops the fertilised egg à embryo, placenta implanted here

Uterus space – (d) sperm cells and egg cells move, embryo develops à unborn child

Cervix – (e) entrance to the uterus

Vagina – (f) collects the sperm cells and allows them to pass through the cervix into the uterus

Before pregnancy, the uterus is no bigger than an orange, but after pregnancy it EXPANDS. 

3.9a

3.9 recall the structure and function of the male and female reproductive systems

Male reproductive organ

Bladder – store urine

Testis – process of meiosis à produce gametes called sperm cells

Epididymis – store sperm cells

Vas Deferens – carry sperm cells to penis during sexual stimulation,

tube pulses and contracts

Prostate – adds 20 – 30% to volume of semen, contain sugars

and it is alkaline à neutralise the acidic secretion in the vagina

Seminal vesicles – also produce sugar based secretion, alkaline, about 70% of semen

Urethra – join the left and right testes, takes semen down the penis, exit for urine

Penis – carry sperm cells into the vagina during sexual intercourse

3.12

3.12 understand how the developing embryo is protected by amniotic fluid

In the uterus space, there is the amniotic fluid, which protects the developing embryo. The protection comes from the fact that the fluid (largely water) cannot be compressed and it absorbs pressure. Any force applied to the uterus wall will be absorbed by the amniotic fluid and prevent damage to the child. An example of such pressure absorber is when you try to kick in the swimming pool. It is difficult to generate a lot of power doing that. 

3.11

3.11 describe the role of the placenta in the nutrition of the developing embryo

The child is in the uterus, which is an environment filled with amniotic fluid. The child cannot digest, breathe or adequately carry out excretion. In order to receive nutrients, the umbilical cord grows out of the embryo, forming a placenta. The child’s blood vessels spread out to form the placenta (not the mother’s blood). The placenta grows into the wall of the uterus. Glucose, amino acids and fats travel through the wall of the uterus into the child’s bloodstream. The placenta has a large surface area and a thin barrier between the mother’s blood and the child’s blood. Nutrients (glucose, amino acids, fats) are given from the mother while excretion (carbon dioxide and urea) are given back to the maternal blood. 

3.24

3.24 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes

Mitosis is cell division that causes growth, an increase in number of cells. A normal cell has diploid number of chromosomes (2n). For humans, this would be 2n = 46. Through mitosis, a cell will divide into two. Each will contain a diploid nucleus. These cells are identical daughter cells. We know that they have the same number of chromosomes and same set of chromosome (i.e. if you choose a random chromosome, you will find an identical version within the cell).

Phases

1)     Interphase – this is when DNA replication takes place. During this process, each chromosome undergoes a copying process to form an identical copy of itself. The pair of chromosomes (exact copies) are held together by centromere. We refer to the copied pair as a pair of chromatids. The replication process takes place inside the nucleus while the nucleus is still intact.

2)     Prophase – we can see the breakdown of the nuclear membrane. Chromosomes are now a pair of visible chromatids.

3)     Late prophase – network of protein molecules begin to form (spindle). These spindle fibres extend from one pole to the other. The chromosome pair moves towards the spindle and join at the centromere.

4)     Metaphase – the pair reaches the middle of the spindle fibre. The characteristics of this phase are that the chromosome is in the middle and the spindle fibre is arranged across the equator of the cell.

5)     Anaphase – the spindle fibre shortens. This pulls one chromatid in one direction and the second one in the other direction. The characteristics of this phase are that the pair move apart, move towards the poles of the cell and they separate.

6)     Telophase – the nucleus begins to reform around the chromosomes at either ends of the cell. Here two nuclei are formed and two sets of chromosomes remain at opposite ends of the cell. 

7)     Cytokinesis – cells split into two. This is not part of mitosis! The reformed nucleus form into two cells when the cytoplasm divides in half. The membrane fuses across the equator forming two new cells, each containing ONE chromosome. In humans, 23 pairs separate all at the same time.

3.16

3.16 describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G)

There are thousands of genesà expand: HELIX à ATGC holding two strands together

The two sugar phosphate backbones are parallel. What hold the two strands together are the bases (adenine, thymine, cytosine and guanine). They hold the helices together by pairing between A & T and G & C.

Looking at the picture on the very right, we can see that the order is ACTGAACCAG. This is the order of bases.

Genes are determined by the order and number of bases, which lead to construction of protein in the cytoplasm into determining characteristics.