SCIENCE AT3 YR10 MHS

Unicellular organism

An organism made up of one cell that reproduces asexually through mitosis.

Multicellular organism

An organism made up of many cells that uses mitosis for growth and repair.

Cell

The basic structural and functional unit of life.

Tissue

A group of similar cells working together to perform a function.

Organ

A structure made of different tissues working together to carry out a function.

System

A group of organs that work together to perform a major body function.

Mitosis

Cell division that produces two diploid cells which are genetically identical to each other and to the parent cell.

Sister chromatids

Identical copies of a chromosome joined at the centromere, separated during mitosis.

Centromere

The region of a chromosome where sister chromatids are joined.

Homologous chromosomes

A matching pair of chromosomes, one derived from each parent.

Diploid number

The full set of chromosomes in a cell; in humans this is 46 (23 pairs).

Diploid

Cells containing two complete sets (2n) of chromosomes.

Meiosis

Cell division that produces four haploid cells which are genetically unique.

Haploid number

Half the normal chromosome set; in humans this is 23.

Haploid

Cells containing only one complete set (n) of chromosomes.

Gametes

The haploid sex cells (sperm and ova) formed during the process of meiosis.

Fertilisation

The uniting of two gametes to produce a zygote.

Crossing-over

A process occurring in meiosis, where genetic material is exchanged between homologous chromosomes.

Zygote

The diploid cell formed during the process of fertilisation.

Purpose of cell division in unicellular organisms

To reproduce and create new individuals.

Purpose of cell division in multicellular organisms

To allow growth and to replace or repair damaged cells.

Reproduction

The biological process by which organisms produce new individuals, either sexually or asexually.

Sexual reproduction

A type of reproduction which involves gametes and produces genetically unique offspring.

Asexual reproduction

A type of reproduction that does not involve gametes and produces genetically identical offspring.

Budding

A type of asexual reproduction, e.g. hydra.

Spores

A type of asexual reproduction, e.g. bread mould.

Binary fission

A type of asexual reproduction, e.g. bacteria.

Fragmentation

A type of asexual reproduction, e.g. worms.

Vegetative propagation

A type of asexual reproduction, e.g. succulents.

Parthenogenesis

A type of asexual reproduction, e.g. lizards.

Advantages of sexual reproduction

Increases variety in offspring.

Disadvantages of sexual reproduction

Requires two parents and is slower.

Advantages of asexual reproduction

Produces genetically identical offspring quickly.

Disadvantages of asexual reproduction

No variation in offspring.

Mitosis vs Meiosis

Mitosis produces 2 diploid daughter cells that are genetically identical; used for growth, repair, and asexual reproduction. Meiosis produces 4 haploid gametes that are genetically different; used for sexual reproduction.

Gonads

Organs that produce gametes in males and females (i.e. testes & ovaries).

Testes (testis)

Male gonads located in the scrotum that produce sperm (male gametes) and male sex hormones.

Scrotum

A pouch outside the body that holds the testes; keeps sperm at a lower temperature than body heat.

Epididymis

A section of tightly coiled tubes in the testes where sperm are stored.

Vas deferens

A narrow tube that carries sperm from the epididymis towards the prostate gland and seminal glands.

Prostate gland and seminal glands

Male glands that add milky fluid to sperm to form semen.

Semen

Mixture of sperm and fluids that activates sperm and is ejaculated from the penis.

Penis

Male organ with spongy erectile tissue that becomes engorged with blood and erect for copulation.

Ovaries

Female gonads inside the body that produce and store ova (female gametes) and secrete female sex hormones.

Ovulation

The release of an ovum from the ovary into the fallopian tube.

Fimbriae

Finger-like projections at the end of the fallopian tube that guide the ovum into the tube.

Fallopian tube (oviduct)

A narrow tube, 10-12 cm long, that transports the ovum to the uterus; site of fertilisation.

Uterus (womb)

A muscular, cone-shaped organ where a fertilised egg implants and develops into an embryo.

Blastocyst

Early stage of development formed by mitosis after fertilisation that embeds in the uterine wall.

Cervix

The lower, narrow part of the uterus that connects to the vagina, protects the uterus, and dilates during birth.

Vagina (birth canal)

A muscular tube that carries the baby from the uterus to the outside during birth.

Vulva

External female genitalia, including the mons pubis, labia minora, and clitoris.

Sperm

Male gamete produced by meiosis with the haploid number of 23 chromosomes.

Ovum (egg)

Female gamete produced by meiosis with the haploid number of 23 chromosomes.

Embryo development

After fertilisation, the zygote undergoes repeated mitotic divisions to form an embryo that will continue developing in the uterus.

Inheritance

The process by which traits are passed from parents to offspring through genetic information carried in genes.

Genetics

The study of heredity.

Gregor Mendel

Scientist who discovered the fundamental principles of inheritance through pea plant experiments.

Factors (Mendel's term)

The discrete units that Mendel proposed control traits; now known as genes.

Gene

A section of DNA that contains coded instructions to synthesise a specific polypeptide, which folds into a protein that determines characteristics.

Allele

The alternate forms of a gene, found at the same location on homologous chromosomes.

Genotype

The combination of alleles present for a particular gene in an organism.

Phenotype

The physical expression of a genotype.

Dominant allele

An allele that masks the presence of a recessive allele.

Recessive allele

An allele that is masked when in the presence of a dominant allele.

Homozygous

Having identical alleles for a single gene. Example: RR (homozygous dominant) or rr (homozygous recessive).

Heterozygous

Having two different alleles for a single gene. Example: Rr (heterozygous).

Trait example

Flower colour, with P = purple (dominant) and p = white (recessive).

Monohybrid cross

A cross between two organisms involving a single gene.

Punnett square

A grid used to show possible allele combinations from parental gametes and predict offspring genotypes and phenotypes.

How to set out a Punnett square

1. Devise a key for alleles. 2. Write genotypes of parents. 3. Draw grid with male gametes on top and female gametes on the side. 4. Fill in boxes with offspring combinations. 5. Write ratios or percentages of genotypes and phenotypes.

Pedigree

A chart used to depict relationships between organisms and how traits are inherited.

Male (pedigree symbol)

Represented by a square.

Female (pedigree symbol)

Represented by a circle.

Unaffected individual

An empty (unshaded) square or circle.

Affected individual

A filled (shaded) square or circle.

Pedigree hint 1

If two unaffected individuals have an affected child, the trait must be recessive.

Pedigree hint 2

If two affected individuals have an unaffected child, the trait must be dominant.

Variation

Differences in traits caused by different alleles of genes; provides diversity within a population.

Natural selection

Process where individuals with beneficial traits survive and reproduce, passing on their advantageous alleles to offspring.

Adaptation

A trait controlled by genes that increases an organism's chance of survival (physical, behavioural, or physiological).

Physical adaptation

A structural trait such as fur colour that provides camouflage.

Behavioural adaptation

A way of acting such as burrowing.

Physiological adaptation

A functional trait such as storing water to resist drought in plants.

DNA (deoxyribonucleic acid)

The molecule found within the nucleus which carries genetic information.

Discovery of DNA structure

In 1953, Watson and Crick determined that DNA has a double helix structure.

Nucleotide

The molecular building block of DNA consisting of a sugar, phosphate, and nitrogenous base.

Nitrogenous bases

The four bases of DNA: adenine (A), thymine (T), cytosine (C), and guanine (G).

Complementary base pairing

Adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).

DNA double helix

The twisted structure formed by double-stranded DNA.

Genetic code

The sequence of DNA bases that provides instructions for how a cell functions.

Chromatin

A complex of DNA and proteins that forms chromosomes; loosely wound and not visible under a light microscope.

Histones

Scaffolding proteins that DNA wraps around to form chromatin, often described as "beads on a string."

Chromosome

A thread-like structure that consists of condensed chromatin; visible during cell division.

Chromosomes under microscope

Visible during mitosis or meiosis when DNA has replicated and condensed.

Karyotype

The complete set of chromosomes of an individual, arranged in numerical order.

Human karyotype

Contains 22 pairs of autosomes and 1 pair of sex chromosomes (XX = female, XY = male).

Analogy for DNA organisation

Base = house, Gene = street, Chromosome = suburb, Full set of chromosomes = city.

DNA replication

The process of making an exact copy of DNA so new cells receive the full genetic instructions.

Semi-conservative replication

DNA replication where each new DNA molecule keeps one original strand and builds one new strand.