Wind-pollinated flower: Pollination occurs because the wind takes the pollen from the anther of one planto to the stigma of another.

Self Pollination: the transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on the same plant. EJ: entra una abeja, se llena de pollen con el anther, y cuando toca el stigma lo llena con el pollen de la propia flor. También puede irse a `otra flor de la misma planta y llenar el stigma con el pollen que recolectó.

HIV is a pathogen that causes an STI (sexually transmitted infections)

- Methods of transmission:

• via exchange of body fluids

• via sharing needles with an infected person

• blood transfusions with infected blood

• from mother to fetus through the placenta

  
  

-The spread of STIs such as HIV are best controlled by:

• Limiting the number of sexual partners an individual has

• Not having unprotected sex, but making sure to always use a condom

• Getting tested if unprotected sex or sex with multiple partners has occurred

• Raising awareness by education programmes

MIRAR VIDEO DE LA FOTO

• the sequence of bases in a gene determines the sequence of amino acids used to make a specific protein

• different sequences of amino acids give different shapes to protein molecules

• DNA controls cell function by controlling the production of proteins, including enzymes, membrane carriers and receptors for neurotransmitters

• most body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs

- diploid nucleus is a nucleus containing two sets of chromosomes

- in a diploid cell, there is a pair of each type of chromosome and in a human diploid cell there are 23 pairs

ROLE OF MITOSIS:

- growth: Mitosis produces new cells, allowing organisms to grow by increasing their cell numbers.

- repair of damaged tissues: When tissues are damaged, mitosis generates new cells to replace the damaged ones, aiding in tissue repair.

- replacement of cells: Mitosis continually replaces old or dead cells in tissues, ensuring the maintenance of healthy tissue function.

- asexual reproduction: mitosis creates genetically identical offspring, as it allows the parent cell to divide and produce new individuals.

----------------------------------------------------------

• the exact replication of chromosomes occurs before mitosis

• during mitosis, the copies of chromosomes separate, maintaining the chromosome number in each daughter cell.

stem cells: unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions

• in early development, the zygote forms an embryo which is a ball of cells that implants into the lining of the uterus

• some pathogens and toxins can pass across the placenta and affect the fetus

• Meiosis is involved in the production of gametes

Genotype: the genetic make-up of an organism and in terms of the alleles present

Phenotype: the observable features of an organism

Homozygous: having two identical alleles of a particular gene.

• two identical homozygous individuals that breed together will be pure-breeding

Heterozygous: having two different alleles of a particular gene

• heterozygous individual will not be pure-breeding

Dominant Allele: an allele that is always expressed if it is present in the genotype

Recessive Allele: an allele that is only expressed when there is no dominant allele of the gene present in the genotype.

Codominance: a situation in which both alleles in heterozygous organisms contribute to the phenotype

sex-linked characteristic: a feature in which the gene responsible is located on a sex chromosome.

• this makes the characteristic more common in one sex than in the other.

- red-green colour blindness is an example of sex linkage

• Use Punnett squares in crosses which result in more than one genotype to work out and show the possible different genotypes

• Interpret pedigree diagrams for the inheritance of a given characteristic

• Use genetic diagrams to predict the results of monohybrid crosses involving codominance or sex linkage and calculate phenotypic ratios

• continuous variation results in a range of phenotypes between two extremes. ej: body length and body mass

• discontinuous variation results
  in a limited number of phenotypes with no intermediates. ej: ABO blood groups, seed shape in peas and seed colour in peas

Mutation: Genetic change

- mutation is the way in which new alleles are formed

- ionising radiation and some chemicals increase the rate of mutation

Gene mutation: a random change in the base sequence of DNA

Sources of Genetic variation:

- meiosis

- mutation

- random fertilization

- random mating

In Natural Selection:

• Individuals in a species show a range of variation caused by differences in genes

• When organisms reproduce, they produce more offspring than the environment is able to support

• This leads to competition for food

• Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce

• Therefore the alleles resulting in these characteristics are passed to their offspring at a higher rate than those with characteristics less suited to survival

• This means that in the next generation, there will be a greater number of individuals with the better adapted variations in characteristics

In selecting Breeding: (Selective breeding means to select individuals with desirable characteristics and breed them together)

1.  selection by humans of individuals with desirable features

2.  crossing these individuals to produce the next generation

3.  selection of offspring showing the desirable features

• Based on the idea that within a species there is always variation and chance mutations, some individuals will develop a phenotype (characteristic) that gives them a survival advantage and therefore will:

  • live longer

  • breed more

  • and be more likely to pass their genes on

- consumers may be classed as primary, secondary, tertiary and quaternary according to their position in a food chain

• Herbivore: an animal that gets its energy by eating plants

• Carnivore: an animal that gets its energy by eating other animals

• decomposer: an organism that gets its energy from dead or waste organic material

• trophic level: the position of an organism in a food chain, food web or ecological pyramid

• They also show interdependence - how the change in one population can affect others within the food web

• For example, in the food web above, if the population of earthworms decreased:

  • The population of grass plants would increase as there are now fewer species feeding off them

  • The populations of frogs and mice would decrease significantly as earthworms are their only food source

  • The population of sparrows would decrease slightly as they eat earthworms but also have another food source to rely on (caterpillars)

  
  

• Most of the changes in populations of animals and plants happen as a result of human impact - either by overharvesting of food species or by the introduction of foreign species to a habitat

• Due to interdependence, these can have long-lasting knock-on effects to organisms throughout a food chain or web

• You cannot change the trophic level of the organisms - they must stay in the same order as in the food chain with producers on the bottom, followed by primary consumers, then secondary consumers, then tertiary consumers

• Generally, the larger an individual organism is, the less of them there are

• Humans are omnivores, obtaining energy from both plants and animals, and this gives us a choice of what we eat

• These choices, however, have an impact on what we grow and how we use ecosystems

• Think of the following food chains both involving humans:

Energy Transfer in a Human Food Chain

wheat  →  cow   →   human

wheat  →   human

• Given what we know about energy transfer in food chains, it is clear that if humans eat the wheat there is much more energy available to them than if they eat the cows that eat the wheat

• This is because energy is lost from the cows, so there is less available to pass on to humans