science - biology - paper 2

• homeostasis and response is keeping conditions in your body cells at the right levels
• control system for homeostasis is keeping your body temp, blood pressure, and water levels constant
• control system is automatic by using nervous system or hormones, the three main parts are the receptor, coordination centres which are the brain and effectors
• how it works:

  • a receptor detects a stimulus which sends information to the coordination centre
  • the coordinator centre receives and processes they information, it then organises a response
  • an effector produces a response, this returns the level to its optimum level
• inheritance: the passing of genetic information from one generation to the next
• dna: is the chemical that all of the genetic material

  gene: is a small section of dna, each gene codes for a particular sequence

  genome: is all the genetic material in an organism, find genes in the genome that are linked to different disease, if scientists can find which gene links to an inherited disease they can develop and treatment
• reproduction:

  sexual production

  • two organisms- mum and dad - are mixed
  • parents produce gametes - egg and sperm cells
  • gamete contain half the number of chromosomes- 23 in egg and 23 in sperm
  • offspring receives a mix of genes so inherits features
  • the mixture of genes produces variation in the offspring
  • flowering plants can reproduce their gametes by egg cells and pollen
• reproduction:

  asexual reproduction

  • happen in mitosis
  • one parent cells make a new cell by dividing into two
  • no fusion
  • no mixing of genes
  • no genetic variation
  • each new cell is genetically identical to the parent cell
• meiosis:

  gametes

  • half the number of chromosomes
  • cells divide by meiosis
  • meiosis only happens in the rep system (organs)
• how meiosis happens

  • parent cells has chromosomes in pairs
  • half come from the fathers testes
  • half come from the mothers ovaries
  • the dna in the parent cell is copied
  • each cell divides and each new cell gets half of the chromosomes cell divides again, then end up with four new daughter cells
  • each gamates only have one single set of chromosome, they are genetically different
• mitosis:

  • two gametes fuse together, this makes a new cell
  • new cell now has the normal amount of chromosomes
  • new cell divides by mitosis many times to produce lots of new cells
  • this now turns into an embryo, as the embryo develops these cells differentiate
• X and Y chromosomes:

  • 23 pairs of chromosomes
  • XX- female
  • XY- male
• phenotype is the physical expression of a gene
• allele is a different version of a gene that codes for a different amino acid
• homozygous is the condition of having two identical alleles of a particular gene
• heterozygous is the condition of having two different alleles for a particular gene
• dominant is when the allele is expressed in the phenotype and is expressed in the phenotype - for example using capital letters
• recessive gene is a gene that is expressed only when the allele is present in the genotype - for example using a small letter
• Embryos can be screened for inherited disorders through a process called embryo screening
• During in vitro fertilisation (IVF), embryos are fertilised in a lab and then placed in the mother's womb
• Scientists can remove a cell from each embryo before they are implanted in the mother to conduct embryo screening
• Embryo screening can detect many inherited disorders
• DNA testing for disorders can also be done on embryos in the womb
• Concerns about embryo screening include ethical considerations and the decisions it may lead to
• Some individuals oppose embryo screening due to the potential consequences of the decisions made based on the screening results
• Embryos identified with 'bad' alleles after screening in IVF may be discarded
• Embryo screening for embryos in the womb could result in the decision to terminate the pregnancy
• Arguments against embryo screening:

  • Implies that individuals with genetic disorders are unwanted, potentially leading to unfair treatment
  • Concerns that people may want to select embryos based on preferred features like eye or hair color
  • Expense of the screening process
• Arguments for embryo screening:

  • Helps prevent individuals from suffering due to genetic disorders
  • Treating disorders is costly
  • Existing laws regulate the extent of embryo screening, such as restrictions on selecting the sex of a baby unless for health reasons
• Organisms of the same species have differences
• Different species look different
• Organisms of the same species will usually look at least slightly different
• Variation within a species can be huge within a population
• Variation can be genetic, caused by differences in inherited genes
• Variation can also be environmental, caused by the conditions in which an organism lives
• Most variation in phenotype is caused by a mixture of genes and the environment
• Mutations are changes to the genome
• A gene can mutate, which is a random change in an organism's DNA that can be inherited
• Mutations mean that the gene is changed, producing a genetic variant (a different form of the gene)
• Most genetic variants have very little or no effect on an organism's phenotype