Biology Term 3 & 4 Flashcards
Define a Hormone:
A chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specified target organs.
What are some differences between the Endocrine and Nervous system?
Endocrine System - This is the transmission of chemicals i.e. hormones, via the blood. They have slow transmission and the hormones that are carried disperse throughout the body. These have long-term effects e.g. cause long term changes during puberty.
Nervous System - The transmission of electrical impulses via the nerves, The transmission is rapid (up to 100 m/s). The impulse is sent directly to the target organ. These impulses have short-term effects e.g. the movement of a finger.
Explain the effects of adrenaline
Adrenaline is the fight or flight hormone. It is secreted from the adrenal glands which are located above each kidney. The effects of glucose are as such:
- Heart beats faster, this is to send more glucose and oxygen to the muscles. This creates a thumping heart sensation
- Faster and Deeper Breathing, this is due to increased oxygenation of the blood and removal of CO2. This targets the breathing centre of the brain. This causes panting.
- Vasoconstriction of arterioles in the skin and digestive system, means more blood is available to reach the muscles. This causes the person to go paler and have a dry mouth.
- Vasodilation of skeletal muscle, Processes such as perilstalsis and digestion slow down so that more energy is available for action. This creates the ‘hollow’ tense feeling in the stomach.
- Muscles tense, ready for immediate action. Causes a tense feeling and shivering.
- Liver will convert glycogen to glucose. This means there is more glucose available in the blood to be converted into energy.
- Conversion of fats in the fat deposits into fatty acids. This means there is more fatty acids available in the blood for muscle contraction.
Explain the effects of insulin
Insulin is made in the pancreas which is both a digestive and endocrine gland. Insulin is produced in the group of cells in the pancreas known as Beta-Islets of of Langerhans. Insulin controls the levels of glucose in the body by the instructing the liver to turn glucose into glycogen when blood sugar levels get too high. Glucose is osmotically active whereas glycogen is not.
Explain the effects of testosterone
Testosterone is produced by the testes. Testosterone allows the production of sperm as well as with secondary sexual characteristics during puberty such as hair growth.
Explain the effects of oestrogen
Oestrogen is produced in the ovaries and help with the maturation of the ova. Like testosterone it also helps with the development of secondary sexual characteristics.
Define homeostasis
It is the maintaining of a constant internal environment.
Describe the structure of the skin
The top layer of skin is known as the epidermis. On the very bottom of this epidermis is the basal layer in which cells are constantly being divided causing older cells to be pushed to the top. These dividing cells also give rise to the hair. In the basal layer and epidermis there is the black pigment, melanin, which determines the darkness of the skin. Under the epidermis is the dermis which contains sweat glands, blood vessels and nerve endings. Under the dermis there is a layer of adipose tissue or fat deposit used to insulate heat.
What happens when the temperature is too low in the body?
- Vasoconstriction of blood vessels occur to reduce the amount of heat lost to the surroundings.
- Sweat production stops so less heat is lost through latent heat of vaporisation.
- Shivering - uncontrollable, involuntary bursts of muscle contractions in the limbs. Heat is released as a result of respiration in the muscles.
- Hairs stand up and erector muscles contract. This traps a layer of heat as it has formed an insulating layer.
What happens when temperature is too high in the body?
Vasodilation of blood vessels - This means that the arterioles widen to allow more warm blood to flow through the blood capillaries near the skin surface. This means heat is lost
Latent Heat of Vaporisation or Sweating - Sweat glands secrete sweat onto the skin surface. When the liquid evaporates it takes heat from the body and cools it down.
Why is the regulation of body temperature important?
Because all chemical reactions that take place in living cells require enzymes. Any extreme changes in temperature from the usual 37°C can slow down or denature these enzymes. For the same reason the pH levels in the body must also be maintained by homeostasis.
Why must the tissue fluid composition be kept steady?
Although the cell membrane controls what enters and exits the cell, the tissue fluid supplies and removes these substances when required. If this tissue fluid were to become too concentrated, it would withdraw water from the cells by osmosis. If the tissue fluid was too diluted, the cells would take up too much water from osmosis and become water-logged and swollen.
What is the brain’s role in the regulation of temperature?
The brain detects any changes from normal by monitoring the temperature of the blood. A region called the hypothalamus contains a thermoregulatory centre in which temperature receptors detect any changes in the blood and co-ordinate a response to them. Thermoreceptors are also found in the skin, which send information about temperature changes to the brain.
Describe the regulation of blood sugar levels
If sugar levels decrease the Beta-Islets of Langerhans release the hormone glucagon. Glucagon induces the liver to convert glycogen into glucose. If sugar levels increase the islets produce insulin which induce the liver to convert glucose to glycogen.
Describe type 1 diabetes, effects and symptoms
It is an autoimmune disease in which the Beta-Islets of Langerhans are destroyed by antibodies produced in the immune system. This means that there is a deficiency of insulin in the body.
Symptoms: Swelling of brain which can lead to death, Patient become thirsty, Frequent Urination, and Confusion.
Treatment: Insulin injections, Controlled Diet
Explain negative feedback
Homeostasis is controlled by negative feedback. Negative feedback is the system of control that causes the body to counteract any deficiencies or surplus of a certain substance in the body. The outgoing impulses counteract the effects that produced the incoming impulses. An example of this is when there is a rise in temperature. This rise triggers responses in the hypothalamus that counteract the rise.
Define tropisms
Tropisms are growth movements related to directional stimuli. Essentially they are a plant’s response to environmental change. Phototropism is a response in which a plant grows towards or away from the direction from which light is coming. Gravitropism is a response in which a plant organ grows towards or away from gravity. If a plant responds by growing towards the stimuli it is ‘positive’ and if against it is ‘negative’.
Advantages of positive phototropism of shoots
By growing towards a light source, a shoot brings its leaves into the best situation for photosynthesis. Similarly, flowers are brought into the best position to be seen and pollinated.
Advantages of negative gravitropism in shoots
These shoots grow vertically. This helps the plant compete for light and CO2. Seed dispersal may also be more effective, and flowers are brought into a better position for insect or wind pollination.
Advantages of positive gravitropism in roots
By growing towards gravity the roots penetrate the soil which gives the plant better anchorage and a better source of water and minerals.
Explain the role of growth substances such as auxin in tropisms
Just as humans have hormones for growth rate and extent of growth, plants have growth substances. Unlike hormones, growth substances are found in regions of actively dividing cells such as the tips and roots rather than a specific organ. Auxin is produced in the meristem of the plant. Auxin allows the cells to elongate by causing the cell wall to acidify (The H+ cause H-bonds to break so the cell wall can elongate). Auxin is unevenly distributed according to stimuli e.g. When a shoot is exposed to light the auxin moves towards the shaded side causing the shaded cells to elongate. This causes the shoot to curve as one side of cells are larger than the other.
Define inheritance
The transmission of genetic information from generation to generation
Define chromosome
A thread-like structure of DNA, carrying genetic information in the form of genes.
Define a gene
A gene is a length of DNA that codes for a protein.
Define allele
An allele are alternative versions of a gene.
Explain the inheritance of sex in humans
Females contain two sex chromosomes called the X chromosome which are of the same size. In males there are two sex chromosomes of different sizes, an X chromosome and a smaller Y chromosome. When gametes are formed they take half the normal number of chromosomes, meaning 23 for humans. All ovum will have their first X chromosome come from the female. However, 50% of sperm have and X chromosome and 50% have a Y chromosome. This means there is equal chance of the offspring being XY or boy or XX or girl.
Explain the genetic code and its relevance to forming and ordering amino acids
A nucleotide carries one of the 4 bases, A, T, G, C. A string of nucleotides holds a sequence of these bases. This sequence forms a code which instructs the cell to make particular proteins. Proteins are made of amino acids which will determine the protein based on their type and sequence which are determined by the base sequences. Each group of three bases stand for one amino acid. This means a gene is a sequence of triplets of the four bases, which specifies an entire protein.
Explain how proteins are made
A molecule called a messenger RNA or mRNA is used to transfer the information of the codes needed to make proteins to where they are needed in the cell. mRNA is much smaller than DNA and only contains one strand. mRNA also carries a U base instead of a T base which is uracil. Uracil attaches to the DNA base A. To pass on the protein code, the double helix of DNA unwinds to expose the chain of bases. One stand acts as a template. A mRNA molecule is formed along part of this strand, made up of a chain of nucleotides with complementary bases to a section of the DNA strand. The protein-carrying mRNA molecule passes out of the nucleus through a nuclear pore on the membrane. Once in the cytoplasm it attaches itself to a ribosome. The mRNA molecule instructs the ribosome to put together a chain of amino acids in a specific sequence, thus making a protein.
Define a haploid nucleus
A nucleus containing a single set of unpaired chromosomes present, e.g. in gametes
Define mitosis
Nuclear division giving rise to genetically identical cells.
What is the function of mitosis?
- growth, repair of damaged tissues
- replacement of cells
- asexual reproduction
Describe the process of mitosis
- Just before the cell divides, thread-like chromosomes appear in the nucleus.
- The chromosomes get shorter and thicker
- Each chromosome replicates itself and makes 2 parallel strands called chromatids.
- The nuclear membrane disappears and fibres pull the chromatids apart to opposite ends of the cell.
- A nuclear membrane forms around each set of chromatids and the cell starts to divide. When the nucleus divides into two, one chromatid from each chromosome goes into each daughter nucleus. These chromatids become chromosomes in each nucleus.
- Cell division is complete giving two ‘daughter’ cells, each containing the same number of chromosomes as the parent cell.
Define meiosis
Nuclear division giving rise to cells that are genetically different.
Describe the process of meiosis
- The chromosomes appear, and just like mitosis the chromosomes shorten and thicken.
- Homologous chromosomes lie alongside each other .
- The nuclear membrane disappears and corresponding chromosomes move apart to opposite ends of the cell. This differs from mitosis as in mitosis, it is the chromatids that are pulled apart.
- The chromosome replicates itself and now consists of two chromatids.
- A second division takes place to separate the newly formed chromatids.
- Four gametes are formed, with each containing only half the original number of chromosomes. This creates variation as the maternal and paternal chromosomes meet in different combinations in the zygote.
Explain how independent assortment during meiosis produces variation in offspring
When homologous pairs of chromosomes line up during meiosis, they do so randomly i.e. in no particular order. This makes the alleles that end up in a gamete are completely random.
Define Genotype
The genetic makeup of an organism in terms of the alleles present
Define Phenotype
The observable features of an organism
Define Homozygous
Having two identical alleles of a particular gene
What is pure breeding?
This is when two identical homozygous individuals breed together to produce the same homozygous alleles.
Define heterozygous
Having two different alleles of a particular gene. The offspring of heterozygous individuals cannot be pure bred.
Define a dominant allele
An allele that is expressed if present
Define a recessive allele
An allele that is only expressed when there are no dominant alleles of the genes present.
What is a test cross and how is it performed?
A test cross is a method of determining the genotype of a phenotypically dominant individual (either Heterozygous or Homozygous dominant). To do this ou must:
- Breed the individual with a homozygous recessive individual.
- If after sufficient offspring is produced and no recessive individuals are produced, it is likely that the individual in question is homozygous dominant as they will always pass down the dominant allele.
- If phenotypically recessive individuals are produced as well, then the individual must be heterozygous, as the recessive allele is passed down to the offspring.
Explain co-dominance with reference to human blood types
Co-dominance is when two dominant alleles are equally and independently expressed. Heterozygous genotypes will have both phenotypes visible. This is seen in human blood types with type A (IA) and type B (BI) being co-dominant. This means that is a person inherits alleles for both group A and group B they will be blood type AB. However, A and B are both dominant to blood type o (i)
Define a sex-linked characteristic
A characteristic which the gene responsible is located on a sex chromosome, which makes it more common in one sex than another.
Explain why traits such as haemophilia and colour-blindness are found more commonly in males
This is because males carry the Y chromosome which is shorter than the X chromosome. This means that if an allele is on the Y chromosome it is expressed, even if it is recessive, as they have nothing to cover the allele. This is not the case in females as they require two recessive alleles to express a trait, and only one dominant allele is needed to mask the other. This also means that if a gene is only found on the Y chromosome only males can have that characteristic as females do not posses the Y chromosome.