Biology Test Year 10

What are some examples of cellular organelles?

Genetic material: DNA or RNA, Cytosol, ribosomes, plasma membrane/ cell membrane NOT THE SAME AS CELL WALL, nucleus, nucleur membrane, mitochondria, chloroplasts, endoplasmic reticulum

Prokaryotic Cells

• a prokaryote is a single-celled organism made out of prokaryotic cells

• do not contain membrane- bound organelles

• examples: bacteria, archaea

Eukaryotic cells

• a eukaryote is an organism made out of eukaryotic cells, e.g humans, animals

difference between animal cell and plant cell

plant cells have a square shape, animal cells have a circle shape. Animal cells lack a cell wall and chloroplasts making them circular.

Phenotype vs genotype

a genotype is the observable characteristics of a organism based on their genotype and environment. A genotype is the sequence of genes responsible for a trait.

what does DNA stand for?

De = Missing or less

oxy = oxygen

ribo = sugar

nucleic = nucleus

Acid = acid

It is the genetic material that is passed on from one generation of organisms to another.

chromatin

Chromatin is the mass of genetic material, ( RNA, DNA AND protein) inside the nucleus: so the mass of DNA inside a cell is in its chromatin

In the nucleus, chromatin is not visible. When the cell divides in two, THAT IS WHEN this chromatin condenses into structures known as chromosomes.

DNA properties

• It carries genetic information for making proteins.

• It replicates itself

DNA is found in the nucleus of most eukaryotic cells AND every cell of the human body EXCEPT red blood cells

What molecules are nucleotides made up of

• a nitrogen base

• a sugar molecule (deoxyribose sugar)

• a phosphate molecule (phosphate group)

Types of nitrogenous bases and bonds

adenine - thymine, 2 hydrogen bonds, called purines

cytosine- guanine, 3 hydrogen bonds, called pyramines

The four types of nitrogen bases link in a specific way ; their chemical structures and hydrogen bond capacities match perfectly, like a lock and key, allowing them to form stable bonds across the DNA double helix

how does the deoxyribose sugar bond with the nitrogenous bases

Covalent bond, makes a very strong bond

what is coiling and folding?

• When the cell gets ready to divide (during prophase of mitosis), the chromatin starts to coil tightly.

• It wraps around histones more compactly and folds into thicker fibres.

how is it very stable

The sugar of one nucleotide is joined to the phosphate of the next nucleotide; covalently

the deoxyribose sugar bond with the nitrogenous bases: covalently

the nitrogenous bases link together via hydrogen bonds

Chromosomes

• Chromosome = DNA + Histone proteins

• Homologous chromosomes are pairs of matching chromosomes in diploid organisms, with one set inherited from each parent

• Chromosomes ensure that DNA is replicated and distributed correctly when the cell divides into two.

• chromosomes are classified by its centromere, the centromere does not have to be located in the centre

what are telomeres?

Telomeres are protective caps made of repetitive DNA sequences and proteins located at the ends of chromosomes

what are the chromosome arms

Chromosomes have sections called arms, the short arm is called the p arm and the long arm is called the q arm

Chromatids

1. When the cell divides in two, the DNA in the cell needs to double in order to have the same amount in both of the two new cells.

2. When this occurs, the chromosomes contain 2 identical copies of the DNA connected by the centromere.

3. Each individual half of the replicated chromosome is known as a chromatid or sister chromatid.

⭐They are still referred to as one chromosome when they are connected by the centromer

autosomes

non-sex chromosomes, first 22 pairs

allosomes

sex chromosomes, last pair x and/ or y

how many chromosomes in human non-sex cell

2n = 46

how are chromosome pairs matched up?

These pairs are matched up according to the length of the chromosome and the position of the centromeres. They also have the same genes in the same places. Chromosomes also display dark bands in specific places . Homologous chromosomes have the same banding pattern. Each chromosome pair consists of one chromosome inherited from the mother, and one from the father.

what are homologous chromosomes?

A homologous pair is:

• One chromosome from your mother

• One chromosome from your father

Homologous chromosomes have the same:

• Length/size

• Shape

• Genes in the same locations (called loci)

• position of centromere

Even though they have the same genes, they can have different versions of those genes (called alleles).

Karyotype

A karyotype is an organized profile of an individual’s chromosomes. Their chromosomes are arranged in pairs, numbered 1-22 (plus X and/or Y).

• The chromosome pairs are organized according to size: chromosome 1 is the largest and chromosome 22 is the smallest.

mutations

Mutations can happen by chance or have a particular cause. • When the cause of the mutation cannot be identified, it is called a spontaneous mutation. • When the cause can be identified, it is referred to as an induced mutation.

A factor that triggers mutations in cells is called a mutagen or mutagenic agent.

Examples of mutagenic agents include:

• radiation, such as ultraviolet radiation, nuclear radiation and X-rays

• chemical substances, such as asbestos, tobacco and benzene (which used to be common in pesticides)

• infectious agents, such as human papillomavirus (HPV).

Changes in the genetic code due to mutations may result in a particular protein not being made or a faulty version being produced.

interphase

Dna duplicates

G1: The cell grows physically larger, increases its supply of proteins, and duplicates organelles.

S stage (synthesis) : replication of DNA

G2: the cell grows further, produces proteins necessary for division, and replenishes energy stores. It also undergoes a final check for DNA damage.

Prophase mitosis

1. Chromatin condenses into VISIBLE chromosomes

2. Nuclear membrane breaks down, allowing chromosomes to move freely

3. Spindle fibres begin to form

4. The nucleolus disappears because The cell is shutting down normal activities (like making ribosomes) and It’s focusing on dividing the chromosomes instead

metaphase in mitosis

1. Chromosomes line up in the centre

2. Spindle fibres attach to each chromosome’s centromere

Each sister chromatid is attached to fibres from opposite poles

Anaphase

1. Sister chromatids separate; The centromere splits, Each pair of sister chromatids is pulled apart, Once separated, each chromatid is now called a chromosome

They seperate through the spindle fibers pulling them to opposite poles

3. Cell elongates, helps move the chromosomes further apart

Telophase in mitosis

1. Chromosomes reach opposite poles, and decondense back into chromatin, nuclear membrane reforms, and nucleolus reappears

Cytokinises

cell’s cytoplasm splits

Prophase I meiosis

1. Chromosomes condense and thicken and appear visible

2. Homologous chromosomes pair up → called synapsis, line up with their homologous chromosomes

3. Form tetrads (4 chromatids total)

4. Crossing over occurs:

   • Chromatids exchange DNA

   • Creates genetic variation

5. Nuclear membrane breaks down to allow the spindle fibers to access chromosomes

Metaphase I

• Tetrads line up in the middle (equator) of the cell

• Orientation is random → called independent assortment

Anaphase 1

• The homologous pairs are pulled apart to opposite poles by spindle fibers. Crucially, the sister chromatids stay together here.

• Each chromosome (still 2 chromatids butterfly shape) goes to opposite poles

Telophase I + Cytokinesis

• Cell splits into 2 haploid cells, and the chromosomes become spaghetti again( chromatin)

• nulcear membrane re forms

• Each cell has:

  • Half the chromosomes

  • Chromosomes still made of 2 chromatids

  • Each cell has 23 butterfly looking chromosomes, 46 chromatids

  • nucleolus comes bek

Prophase II

• Chromosomes condense again, from chromatin to chromosome

• Nuclear membrane breaks down to allow spindle fibers to access chromosomes

• spindle fibers begin to form

Metaphase II

chromosomes line up at the equator, and attach to the spindle fibers

Anaphase II

1. The centromeres finally break, and sister chromatids are pulled apart to opposite poles by spindle fibers.

• Sister chromatids separate and move to opposite poles

• Now they are called individual chromosomes

Telophase II & Cytokinesis:

• nuclear membrane comes bek

• nucleolus comes back

• The cells divide again, resulting in four daughter cells, each with a single set of unique chromosomes.

• result: 23 single- stranded chromosomes in the form of chromatin in their new cells

diploid

• Have 2 sets of chromosomes

• Total = 46 chromosomes

• Come in homologous pairs (one from each parent),

Total diploid number, 2n= 46

Haploid

Only sex cells (gametes) are haploid

• Sperm and egg cells

• Have 23 chromosomes (n)

• Only one set

👉 The haploid number is:

the number of chromosomes in a gamete (sex cell)

• It represents one complete set of chromosomes

In humans:

• Haploid number = 23

male reproductive structures

stamens

female reproductive structures

carpels

genome

A genome is the complete set of genetic instructions—all the DNA—contained within an organism's cells. It includes all genes and non-coding sequences required to build, maintain, and operate that organism. In humans, this consists of 23 pairs of chromosomes ( 2n = 46) plus mitochondrial DNA, totaling 3.2 billion base pairs.

allele

alternative form of a gene

everyone inherites one allele from each parent

alleles for the same gene are found on the same loci ( position ) on a chromosome

homozygous

2 identical alleles for a trait

heterozygous

2 different alleles for a trait

autosomal dominant

 If both parents are affected the offspring may be unaffected

 If neither parent is affected the offspring must be unaffected

 If an offspring is affected there must be an affected parent

autosomal recessive

If both parents are affected the offspring must be affected

If neither parent is affected the offspring may be unaffected

If an offspring is affected there may be an affected parent

The trait can skip a generation

x linked dominant

If a male is affected, his mother must be affected

If a male is affected, his daughters must be affected
If a female is unaffected, her father must be unaffected
If a female is unaffected, her sons must be unaffected
The trait cannot skip a generation

x linked recessive

If a female is affected, her father must be affected
If a female is affected, her sons must be affected
If a male is affected, his mother may be affected
The trait can skip a generation

y linked

Only males can show the trait

All males in a lineage will show the same phenotype

The trait cannot skip a generation