GCSE Biology

Eukaryotic Cell

Cell with a true nucleus surrounded by a nuclear membrane and contains membrane-bound organelles such as mitochondria and endoplasmic reticulum. Generally larger and more complex than prokaryotic cells, such as animal, plant, fungal, and protist cells.

Prokaryotic Cell

Cell without a nucleus or other membrane-bound organelles. Single circular strand of DNA located in the cytoplasm. Smaller and simpler than eukaryotic cells, such as bacteria and archaea cells.

Animal Cell

Eukaryotic cell that makes up animals. Has a nucleus containing genetic material, cytoplasm, cell membrane, mitochondria, and ribosomes. No cell wall, chloroplasts, or large permanent vacuole, unlike plant cells.

Cell Membrane

A semipermeable barrier surrounding the cell that controls what substances enter and leave, such as oxygen, glucose, and waste products. Composed of a phospholipid bilayer with proteins.

Cytoplasm

Jelly-like substance inside the cell where most chemical reactions take place. Contains enzymes that speed up reactions and supports the organelles within the cell.

Mitochondria

Small organelles where aerobic respiration takes place, releasing energy for the cell’s activities from glucose and oxygen. Powerhouse of the cell, role in energy production.

Nucleus

Membrane-bound organelle that contains the cell’s genetic material (DNA), organized into chromosomes. Controls activities of the cell by regulating gene expression and protein synthesis.

Plant Cell

Eukaryotic cells that make up plants containing a nucleus, cytoplasm, cell membrane, mitochondria. Also unique to it, the cell contains a cell wall, chloroplasts, and permanent vacuole

Cell Wall

Rigid outer layer found in plant, fungal, and bacterial cells. Made of cellulose and supports and protects the cell, maintains its shape and prevents it from bursting when water enters by osmosis.

Permanent Vacuole

Large, fluid-filled sac in plant cells containing cell sap (water, sugars, and salts). Helps maintain turgor pressure- firm cell and supports plant.

Chloroplasts

Green, disc-shaped organelles in plant cells containing chlorophyll, which absorbs light for photosynthesis. Convert light energy into chemical energy (glucose), which the plant uses for growth and respiration.

Bacteria Cell

Prokaryotic cells that do not have a nucleus or membrane-bound organelles. Include a cell wall, cell membrane, cytoplasm, single circular DNA strand in cytoplasm, plasmids, may have flagella for movement. Smaller and simpler.

Tissue

Group of similar cells that work together to perform a specific function. Cells are adapted to carry out their function efficiently. Inlcudes muscular, glandular, and epithelial tissue.

Organ

A structure made of different types of tissue working together to perform specific functions. Each tissue within the organ contributes to the organ’s overall function.

Organ System

A group of organs working together to perform major life processes for the organism.

Muscular Tissue

Composed of muscle cells containing protein filaments (actin and myosin) that slide past each other, allowing contraction. Helps with the movement of the body and substances within the body.

Glandular Tissue

Composed of cells that are specialized to secrete substances such as enzymes, hormones, mucus, and acids. Found in glands and within organs. Involves exocrine secretion and endocrine secretion.

Epithelial Tissue

Layers of tightly packed cells cover surfaces inside and outside the body. Protects, absorbs, secrets, and forms barriers.

Transport of Substances

Across cell membranes there is: active transport, diffusion, and osmosis.

Diffusion

The net movement of particles (molecules or ions, not including water) from an area of higher concentration to an area of lower concentration down the concentration gradient. Passive process, due to random movement of particles, and continues until equilibrium is reached. Steeper gradient, higher temperature, larger surface area & thinner membrane = faster diffusion rate.

Osmosis

Diffusion of water molecules across a partially permeable membrane from a region of higher water potential to a region of lower water potential. Passive process, larger solute molecules cannot pass. In plant cells, water enters by osmosis, filling the vacuole, and the cell becomes turgid. If water is lost by osmosis, cell becomes flaccid and may plasmolyse. In animal cells, if water enters by osmosis, cell may swell and burst (lysis). If water leaves by osmosis, the cell shrinks and becomes crenated.

Active Transport

Movement of particles from an area of lower concentration to an area of higher concentration against the concentration gradient, using energy from respiration (ATP). Active process, requires energy provided by the mitochondria within the cell. Requires carrier proteins in the cell membrane to transport specific molecules or ions.

The Cell Cycle

Interphase (longest stage):

• Cell grows and carries out normal functions

• DNA replicates to form two copies of each chromosome

• Organelles replicate and energy stores increase

Mitosis:

• Nucleus divides

Cytokinesis:

• Cytoplasm and cell membrane divide, forming two identical daughter cells.

Helps growth, repairs damaged tissue, and in some organisms, is used for asexual reproduction.

Mitosis

Cell division that produces two genetically identical diploid daughter cells with the same number of chromosomes as the parent cell.

Prophase: chromosomes condense, nuclear membrane breaks down

Metaphase: chromosomes align along the equator of the cell, attached to spindle fibres

Anaphase: sister chromatids are pulled apart to opposite poles

Telophase: Nuclear membranes reform around the chromosomes at each pole

Used for growth, repair, and asexual reproduction

Meiosis

Cell division that produces four genetically different haploid gametes with n DNA.

Meiosis I: chromosomes pair up and exchange genetic material (crossing over), then separate into two cells

Meiosis II: Similar to mitosis, sister chromatids separate

Result: Four non-identical haploid gametes

Asexual Reproduction

Reproduction involving only one parent, producing offspring that are genetically identical to the parent, no fusion of gametes, and uses mitosis for cell division. Fast and efficient, less energy to find a mate, and common in single-celled organisms. However, no genetic variation.

Sexual Reproduction

Reproduction involving the fusion of male and female gametes producing genetically varied offspring. Uses meiosis to produce gametes, which fuse during fertilization. Genetic variation in offspring, but requires two parents, more energy, and slower reproduction.

Sex Determination

Biological process that determines whether an individual develops as male or female, based on their sex chromosomes. Humans have 22 pairs of autosomes, 1 pair of sex chromosomes. Females XX, Males XY. All eggs carry an X chromosome from the mother, and sperm can carry either X or Y, and thus determines the sex of the offspring. Some genes are carried on the sex chromosomes, typically X-linked recessive conditions, which men are more likely to express.

DNA

A large, complex molecule that carries genetic information. Made of two strands forming a double helix. Composed of nucleotides, each containing a phosphate group, deoxyribose sugar, and a nitrogenous base (A, T, C, G). DNA carries instructions for making proteins.

Chromosome

Long, coiled DNA molecules wrapped around histone proteins. Contain many genes along their length. Humans have 23 pairs, and during mitosis or meiosis, chromosomes become visible and condensed.

Gene

Short sections of DNA on a chromosome that code for a specific protein. Each gene controls production of specific proteins, which determine characteristics.

Allele

Different versions of the same gene. Can be Dominant or recessive. So gene for eye color can have an allele for brown eyes and an allele for blue eyes.

Genotype

The genetic makeup of an organism, describes the alleles such as AA, Aa, or aa.

Phenotype

The physical appearance of characteristic shown by the organism, determined by genotype and environment. The physical manifestation of the genotype.

Homozygous

Individuals with two identical alleles, AA, aa.

Heterozygous

Individuals with two different alleles for the same trait, Aa.

Genetic Pedigree

A family tree diagram that shows how a particular genetic trait or disorder is inherited across generations.

Circle = Female

Square = Male

Shade = Affected

Unshaded = Unaffected

Roman Numerals = Generations

Half-shaded = Carriers (sec-linked or recessive conditions)

Dominant = Appears every generation

Recessive = Can skip generations

Cystic Fibrosis

Autosomal recessive disorder, needs 2 recessive alleles to express the phenotype. Carriers do not show symptoms.

Polydactyly

Autosomal dominant disorder, at least one dominant allele needed to express the phenotype.

Huntington’s Disease

Autosomal dominant disorder, at least one dominant allele needed to express the phenotype.

Haemophilia

Sex-linked (X) recessive disorder, blood clotting. more common in males as they only have one X chromosome. Females must inherit two faulty X alleles to have haemophilia, which is rare. if they have one, then they are carriers.

Genome

The entire genetic material of an organism, including all the DNA in every cell, genes and non-coding alike.

Nucleotide

Basic building block of DNA & RNA. Each nucleotide is made of: phosphate group, deoxyribose sugar (DNA), and a nitrogenous base. Nucleotides join to form the DNA double helix with phosphate-sugar backbones and bases inside.

Complementary Base Pairing

Specific pairing of nitrogenous bases in DNA that holds the two strands of the helix together.

Adenine & Thymine (2 H-bonds)

Cytosine & Guanine (3 H-bonds)

Ensures that DNA can be copied and reproduced with minimal errors.

Protein Synthesis

How cells make proteins from the instructions in DNA. Replication, transcription, and translation.

Transcription (in the nucleus):

• DNA code copied into mRNA

• DNA unzips, exposing template strand

• mRNA strand built using complementary base pairing

• mRNA leaves nucleus via nuclear pores into the cytoplasm

Translation (in the cytoplasm @ribosomes)

• mRNA attaches to a ribosome

• ribosome reads mRNA codons (3 bases/t)

• tRNA brings amino acids to the ribosome

  • each tRNA has an anticodon complementary to the mRNA codon

  • ensures correct amino acids are brought in sequence

• Amino acids join by peptide bonds, forming poly peptide chain —> folds into functional protein

Central Dogma

Flow of genetic information in cells:

DNA —> Transcription —> RNA —> Translation —> Protein

DNA contains genetic instructions —> transcribed into mRNA —> translated into proteins, which determine cell structure and function

Genetic Mutation

A change in the DNA sequence of an organism’s genome. Can occur spontaneously during DNA replication or be caused by mutagens. This changes the sequence of bases, and can alter the amino acid sequence of a protein, potentially affecting its function. Most of the time, nothing happens. Rarely, they have a small +- effect, and even more rarely, they will determine the phenotype.

Genetic Engineering

Direct manipulation of an oragnism’s genome using biotechnology to alter its characteristics by adding, removing, or modifying genes. Can help produce useful substances, improve crop yield and resistance, and research gene functions and treatments for genetic disorders.

• Identify and isolate the desired gene

• Cut gene using restriction enzymes

  • produces sticky ends, making it easier to join the gene into the vector DNA

• Insert the gene into a vector

  • common vectors include plasmids and viruses

  • vector DNA also cut using the same restriction enzymes to produce complementary sticky ends

  • desired gene is joined into the vector using DNA ligase

  • results in Recombinant DNA

• Transfer the vector into the host cell

• Selection of successfully modified cells

• Expression of the gene

  • host cell transcribes and translates the inserted gene

Recombinant Cell

A cell that contains DNA from different sources combined artificially. Occurs after successful genetic engineering.

Transgenic Organism

An organism that contains a gene(s) transferred from another species. This gene is stably incorporated into the organism’s genome and inherited by its offspring.

Stem Cell

Undifferentiated cells that can divide to produce more stem cells or differentiate into specialized cell types. Embryonic stem cells are found in early day embryos and can become any specialized cell in the body- used for regenerative medicine but raise ethical concerns. Adult Stem Cells (tissue) found in certain tissues, and can differentiate into a limited range of specialized cells. Induced Pluripotent Stem Cells are adult body cells reprogrammed in the lab to behave like embryonic stem cells.

Selective Breeding

Artificial selection, where humans actively choose which organisms with desired characteristics will reproduce to pass on those traits to the next generation. In agriculture for crops, farm animals, and pets. Can produce organisms with desirable characteristics quickly compared to natural evolution, but reduced genetic variation —> inbreeding can occur, less adaptation capability.

Natural Selection

Process where organisms with traits better suited to their environment are more likely to survive, reproduce, and pass on their genes, while those less suited are less likely to survive. Mechanism for evolution proposed.

Variation

Differences between individuals of the same species, essential for natural selection to operate.

Genetic Variation:

Cause by differences in genetic materials (alleles) due to mutations, meiosis, and fertilization, and inherited from parents to offspring.

Environmental Variation

Caused by environmental factors during an organism’s lifetime, not inherited. Most phenotypic traits are influenced by both genetics and environment.

Discrete Variaition

Distinct categories, no intermediates. Controlled by a single or a few genes, and not affected by the environment.

Continuous Variation

Range of values with no distinct categories controlled by many genes, and influenced by environment.

Enzyme

Biological catalysts made of proteins that speed up rate of chemical reactions in living organisms without being used up. Lowers activation energy required for reactions, important in digestion, respiration, DNA replication, photosynthesis, etc…

Active Site

Specific region on the enzyme´s surface where the substrate binds. Shape of the active site is complementary to the substrate, and determined by the enzyme´s tertiary structure (protein folding).

Lock and Key Model

Enzyme action has an active site (lock) which is a fixed, specific shape. Substrate (key) fits exactly into the active site. Enzyme-substrate complex forms, explains enzyme specificity.

Induced Fit Model

Active site is flexible and molds around the substrate when it binds. Substrate induces a slight change for a tighter fit in the active site, so enzymes can be very specific but also adjust slightly to subtrates.

Denature

When the enzyme’s active site changes shape permanently, preventing substrate binding. Due to high temperatures and extreme pH levels, loosing catalytic ability of denatured enzymes.

Digestive Enzyme

Enzymes that break down large, insoluble food molecules into smaller ones that can be absorbed into the bloodstream. Produced by glands and cells lining the gut.

Amylase

Enzyme that breaks down starch into maltose. produces in salivary glands, pancreas, and small intestine, and 7pH optimal pH in mouth and small intestine.

Protease

Enzyme that breaks down proteins into amino acids. Produced in the stomach, pancreas, and small intestine. Works in acid 2 pH stomach and alkaline 8 pH small intestine.

Lipase

Enzyme that breaks down lipids (fats and oils) and produces fatty acids and glycerol. Produced in the pancreas and small intestine, and works in the alkaline 8 pH small intestine.

Aerobic Respiration

A chemical process in cells that releases energy from glucose using oxygen.

Glucose + Oxygen —> Carbon Dioxide + Water + Energy

C6H12O6 + 6O2 —> 6CO2 + 6H2O + ATP

Occurs in the mitochondria of cells, to release energy for cellular processes

Takes place in plants and animals.

Anaerobic Respiration

The release of energy form glucose without using oxygen, occurs when oxygen supply cannot meet demand.

Glucose —> Lactic acid + Energy

Incomplete breakdown of glucose, less energy than aerobic respiration, and lactic acid can cause muscle fatigue and cramp

Occurs in both plants and animals

The Nervous System

Communication system that uses electrical impulses to detect and respond rapidly to stimuli, enabling fast, short-term responses.

Receptors

Specialized cells that detect changes in the environment called stimuli found in sense organs.

Sense Organ

Organs that contain receptor cells: eyes, ears, skin, tongue, nose.

Central Nervous System

Consists of the brain and spinal cord to process information from receptors and coordinate a response in reflex arcs and voluntary responses.

Neurons

Nerve cells that transmit electrical impulses rapidly around the body.

Synapse

A gap between two neurons where chemical neurotransmitters are released to pass on the signal.

Sensory Neuron

Carriers impulses from receptor to the CNS, has a cell body in the middle and long dendron.

Relay Neuron

Only found in the CNS, connects sensory neuron to motor neuron, short, and often involved in reflexes.

Motor Neuron

Carries impulses from the CNS to an effector (muscle or gland), triggering a physical response.

Reflex Arc

An automatic, rapid response to a stimulus that bypasses conscious brain involvement. Important to protect the body from harm.

Stimulus —> Receptor —> Sensory Neuron —> Relay Neuron (CNS) —> Motor Neuron —> Effector —> Response

Pupillary Light Reflex

A reflex that adjusts the pupil size in response to light intensity. Bright light:

Photoreceptors —> impulse to brain —> iris contract muscles —> pupil constricts.

Dim Light:

Less light detected —> radial muscles contract —> pupil dilates.

To protect retina and control amount of light entering the eye.

The Respiratory System

Body system responsible for gas exchange, allowing oxygen to enter the bloodstream and carbon dioxide to be removed. Main organs include nose, lungs, diaphragm, and alveoli.

The Lungs

Pair of spongy, elastic organs in the thorax responsible for inhaling oxygen and exhaling carbon dioxide. Enclosed by the ribcage and aided by the diaphragm during breathing.

Alveoli

Tiny air sacs in the lungs where gas exchange occurs via diffusion. Oxygen diffuses into capillaries from the alveolar air, Carbon dioxide diffuses out of blood into the alveoli. Large surface area.

Surface Area

A larger surface area allows for more efficient diffusion of gases. Millions of alveoli in lungs create huge surface area, making O2 & CO2 exchange quick and efficient. Surface area is directly related to rate of diffusion.

The Circulatory System

Transports oxygen, carbon dioxide, nutrients, hormones, and waste around the body via blood. it consists of the heart, blood vessels, and blood.

Heart

Muscular organ that pumps blood throughout the body. it has four chambers: right atrium, right ventricle, left atrium, left ventricle. Left side: oxygenated. right side: deoxygenated.

Superior & Inferior Vena Cava

SVC: from upper body/head

IVC: from lower body.

Large veins bringing deoxygenated blood from the body to the right atrium.

Right Atrium

Receives deoxygenated blood from SVC/IVC and passes it to the right ventricle.

Right Ventricle

Pumps deoxygenated blood to the lungs through the pulmonary arteries.

Pulmonary Arteries

Carry deoxygenated blood from the right ventricle to the lungs for gas exchange.

Lungs

Where gas exchange occurs, CO2 leaves & O2 enters the blood.

Pulmonary Veins

Returns oxygenated blood from the lungs to the left atrium.

Left Atrium

Receives oxygenated blood from pulmonary veins, passes it to the left ventricle.

Left Ventricle

Pumps oxygenated blood to the entire body via the aorta, high pressure so thicker wall.

Aorta

Main artery carrying oxygenated blood from the left ventricle to the body.

Double Circulatory System

Pulmonary circulation: heart —> lungs —> heart

Systematic circulation: heart —> body —> heart

Allows for high-pressure delivery to the body and efficient oxygenation in the lungs.

Sino-Atrial Node

Natural pacemaker, located in the right atrium. Sends electrical impulses that cause the atria to contract.

Atrio-Ventricular Node

Receives impulse from SAN and delays it briefly before sending it to the ventricles, allowing atria to fully contract first.

Electrocardiogram

Machine that records the electrical activity of the heart. Shows heart rhythm, detects irregularities or heart attacks.

Arteries

Carry blood away from the heart. High pressure, thick muscular walls, small lumen, usually carry oxygenated blood.

Veins

Carry blood to the heart, low pressure, valves to prevent backflow. Thin walls, large lumen, usually carries deoxygenated blood.

Capillaries

Tiny vessels where exchange of gases, nutrients, and waste occurs. 1 cell thick, short diffusion distance. Connects arteries to veins.