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Growth of the pollen tube and its entry into the ovule followed by fertilization:

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Growth of the pollen tube and its entry into the ovule followed by fertilization:

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Insect pollinated flowers are adapted to allow insects to collect pollen

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Advantages & Disadvantages of Asexual Reproduction

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Advantages & Disadvantages of Asexual Reproduction

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Advantages & Disadvantages of Sexual Reproduction

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Advantages & Disadvantages of Sexual Reproduction

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Animal-Pollinated Flowers: Attractive, colorful, fragrant, sticky pollen, nectar-producing. This is to attract and facilitate interactions with animal pollinators, ensuring effective pollen transfer (use animals to transfer pollen).

Wind-Pollinated Flowers: Plain, small, not fragrant, dry pollen, no nectar. This is to optimize the dispersal of pollen through the wind, which does not require attracting animals (use wind to transfer pollen).

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there has to be two parents

Sexual reproduction is a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other

FERTILISATION is defined as the fusion of gamete nuclei, and as each gamete comes from a different parent, there is variation in the offspring

Gametes: sexual cells (sperm cell and egg cells)

The offspring is not the same as the parent genetically

The nuclei of gametes are haploid and the nucleus of a zygote is diploid

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pollination: The transfer of pollen grains from an anther to a stigma

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pollination: The transfer of pollen grains from an anther to a stigma

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Insect pollinated flowers: Pollination occurs because the insect translates the pollen form one flower to the stigma of another.

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

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Wind pollinated flowers are adapted so that wind can easily catch pollen grains and carry them to the stigmas of other flowers

The anthers and stigmas of wind pollinated flowers hang outside the flower so that:

pollen can easily be blown away by the wind

pollen can easily be caught by the stigmas of other flowers

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fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule

For successful seed germination, seeds need the right amount of water, enough oxygen, and a suitable temperature. The three factors must be present for successful germination.

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cross pollination: pollen is transferred from the anther of one plant to the stigma of another plant of the same species. Ej: una abeja va de una flor de la planta, agarra el pollen y lo lleva a otra flor de otra planta de la misma especie.

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.

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Starts in early adolescence in girls (around age 12) and is controlled by hormones

The average menstrual cycle is 28 days long

Ovulation (the release of an egg) occurs about halfway through the cycle (day 14) and the egg then travels down the oviduct to the uterus

Failure to fertilise the egg causes menstruation (commonly called a period) to occur - this is caused by the breakdown of the thickened lining of the uterus

Menstruation lasts around 5 - 7 days and signals the beginning of the next cycle

After menstruation finishes, the lining of the uterus starts to thicken again in preparation for possible implantation in the next cycle

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HIV (Human Immunodeficiency Virus) infection may lead to AIDS (Acquired Immunodeficiency Disease).

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

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A process by which a seed develops into a new plant typically involving the growth of the embryo under right conditions.

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chromosomes are made of DNA, which contains genetic information in the form of genes

Gene: a length of DNA that codes for a protein

Allele: an alternative form of a gene

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

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GCSE Biology - DNA Part 2 - Alleles / Dominant / Heterozygous / Phenotypes and more!  #64

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Females have the sex chromosomes XX

Males have the sex chromosomes XY

As only a father can pass on a Y chromosome, he is responsible for determining the sex of the child

He does this because

He produces (ejaculates) around 250 million sperm cells during sexual intercourse

Of those, half (125 million sperm) will be carrying his X chromosome

If one of these sperm fertilises the egg, the fetus will be female

The other 125 million of his sperm will be carrying his Y chromosome

Which will result in a male fetus if one of these fertilises the egg

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https://youtu.be/ubdoUqmNF98?si=19iWN91VSBnOKNqQ   muchos detalles que no se necesitan

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the gene coding for the protein remains in the nucleus

messenger RNA (mRNA) is a copy of a gene

mRNA molecules are made in the nucleus

and move to the cytoplasm

the mRNA passes through ribosomes

the ribosome assembles amino acids into protein molecules

the specific sequence of amino acids is determined by the sequence of bases in the mRNA

(knowledge of the details of transcription or translation is not required)

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- a haploid nucleus is a nucleus containing a single set of chromosomes

- 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

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Some changes occur to both boys and girls, including growth of sexual organs and growth of body hair

Emotional changes also occur due to the increased levels of hormones in the body

These include more interest in sex and increased mood swings

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Asexual Reproduction: a process resulting in the production of genetically identical offspring from one parent

Only 1 parent required

The offspring is exactly the same to the father (clone)

Asexual reproduction does not involve sex cells or fertilisation

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mitosis: is a nuclear division giving rise to genetically identical cells

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.

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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

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Fertilisation: the fusion of the nuclei from a male gamete (sperm) and a female gamete (egg cell)

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

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Umbilical cord: Connects the fetus to the placenta, transporting oxygen, nutrients, and waste between the fetus and the mother.

Placenta: Facilitates the exchange of oxygen, nutrients, and waste between the mother and fetus while also producing hormones that support pregnancy.

Amniotic sac: Surrounds and protects the developing fetus, providing a physical barrier from external injury.

Amniotic fluid: Cushions the fetus, allows free movement, and helps maintain a stable temperature inside the womb.

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Meiosis: a reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells

Meiosis is involved in the production of gametes

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Inheritance: the transmission of genetic information from generation to generation.

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

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Explain how to use a test cross to identify an unknown genotype

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

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Variation: differences between individuals of the same species

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

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adaptive feature: an inherited feature that helps an organism to survive and reproduce in its environment.

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Plants adapted to live in extremely wet conditions

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Plant adapted to live in extremely dry conditions

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Adaptation: the process, resulting from natural selection, by which populations become more suited to their environment over many generations

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

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Example of Natural Selection: development of strains of antibiotic resistant bacteria

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Example of Natural Selection: development of strains of antibiotic resistant bacteria

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EXAM TIP

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

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Artificial Selection & Natural Selection differences

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Artificial Selection & Natural Selection differences

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1. Outline how selective breeding by artificial selection is carried out over many generations to improve crop plants and domesticated animals and apply this to given contexts

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the Sun is the principal source of energy input to biological systems

Energy flows through living organisms

- Including light energy from the Sun and chemical energy in organisms

- Energy is eventually transferred to the environment eg. as heat

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PARA ENTENDER: Food webs give us a lot more information about the transfer of energy in an ecosystem

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

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Food Chain: showing the transfer of energy from one organism to the next, beginning with a producer

Food Web: a network of interconnected food chains and interpret food webs

a producer is an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis

a consumer is an organism that gets its energy by feeding on other organisms

- 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

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Pyramids of biomass provide a much better idea of the quantity of the plant or animal material at each level of a food chain and therefore are a better way of representing interdependence within the food chain

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Rules to remember when drawing a pyramid of numbers:

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

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The majority of the energy an organism receives gets ‘lost’ (or ‘used’) through:

making waste products eg (urine) that get removed from the organism

as movement

as heat (in mammals and birds that maintain a constant body temperature)

as undigested waste (faeces) that is removed from the body and provides food for decomposers

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