Biology IGCSE: Organisation of the Organisms

Comprehensive vocabulary flashcards covering the organisation of organisms, cell structures, specialised cells, tissues, and organ systems for IGCSE Biology Paper 2 Extended.

Red blood cell

A specialised animal cell that transports substances such as oxygen in the blood; it has a biconcave shape with a thin region in the cell centre and lacks a nucleus.

Root hair cell

A specialised plant cell located on the outer surface of roots with a long hair-like extension that increases surface area for the absorption of water and mineral ions.

Xylem vessel

A non-living plant transport tissue that conducts water and dissolved mineral ions and provides mechanical support to the plant; it lacks a nucleus and cytoplasm.

Cell membrane

A partially permeable boundary present in plant, animal, and bacterial cells that encloses the cytoplasm and controls the entry and exit of substances.

Cell wall

A rigid layer situated outside the cell membrane in plant and bacterial cells that provides structural support; it is absent in animal cells.

Chloroplast

A plant cell organelle located in the cytoplasm containing chlorophyll, where photosynthesis occurs and sugars are made.

Mitochondrion

An intracellular organelle found in eukaryotic cells that functions as the primary site of aerobic cellular respiration to produce energy.

Spongy mesophyll cell

A loosely arranged photosynthetic plant leaf cell containing a cell wall, cell membrane, vacuole, cytoplasm, and chloroplasts, surrounded by air spaces for gas exchange.

Palisade mesophyll cell

A specialised columnar plant leaf cell located beneath the upper epidermis that contains many chloroplasts (typically around $17$) to maximise sugar production via photosynthesis.

Iodine solution

A chemical testing reagent that changes colour from yellow-brown to blue-black in the presence of starch.

Starch

A storage carbohydrate synthesized and stored in plant leaf chloroplasts that turns iodine solution blue-black upon staining.

Vacuole

A large central fluid-filled space within plant cells containing cell sap that maintains turgidity; smaller and temporary vacuoles may occur in some animal cells.

Cytoplasm

A jelly-like fluid enclosed by the cell membrane where organelles reside and where cellular chemical reactions take place.

Nucleus

A membrane-bound organelle that contains genetic material and directs cell activities; present in eukaryotic cells (such as liver and root hair cells) but absent in mature red blood cells, xylem vessels, and bacteria.

Bacterial cell

A unicellular organism featuring a cell wall, cell membrane, cytoplasm, and circular DNA, but lacking chloroplasts and a true membrane-bound nucleus.

Bacterial DNA

The circular strand or loop of genetic material located freely within the cytoplasm of a bacterium without being enclosed inside a nuclear membrane.

Tissue

A group of similar specialised cells that work together to perform a specific function, such as xylem, muscle tissue, or a group of palisade cells.

Organ

A distinct structure composed of different tissues working together to carry out specific functions, such as the stomach, brain, liver, leaf, or root.

Organ system

A group of related organs that cooperate to perform a major body function, such as the reproductive system or the breathing system.

Hierarchy of organisation

The sequence of increasing structural complexity in living organisms: $\text{cell} \rightarrow \text{tissue} \rightarrow \text{organ} \rightarrow \text{organ system} \rightarrow \text{organism}$.

Ciliated cell

A specialised epithelial cell lining the trachea that features hair-like surface projections adapted to sweep mucus and trapped dust particles away from the lungs.

Cilia

Microscopic, hair-like extensions on the free surface of ciliated epithelial cells that rhythmically beat to propel fluids and particulate matter along respiratory passages.

Motor (effector) neurone

A specialised nerve cell with a cell body containing a nucleus, dendrites, and an elongated axon that conducts electrical impulses to effectors such as muscles or glands.

Liver cell

A typical animal cell possessing a cell membrane, cytoplasm, and a nucleus, but completely lacking a cell wall, chloroplasts, and a large central vacuole.

Amoeba

A single-celled eukaryotic organism that feeds via food vacuoles and performs gas exchange directly through its cell membrane.

Gas exchange in Amoeba

The passive diffusion of oxygen into the cell and carbon dioxide out of the cell across the cell membrane, reflecting cellular respiration and excretion.

Phloem

A plant vascular tissue responsible for the translocation of sucrose and amino acids between plant organs.

Leaf

A plant organ comprised of multiple specialised tissues (including epidermis, mesophyll, xylem, and phloem) dedicated to photosynthesis and gas exchange.

Root

A plant organ adapted for anchoring the plant and absorbing water and dissolved mineral ions, housing tissues such as root hairs and xylem vessels.

Sperm cell

A specialised male gamete possessing a flagellum, cytoplasm, and a haploid nucleus, functioning in sexual reproduction.

Muscle cell

An elongated animal cell adapted to contract and produce movement; it utilizes oxygen rapidly during contraction, causing blood leaving the contracted muscle to carry lower percentages of oxygen.

Guard cells

Specialised photosynthetic cells flanking stomatal pores on leaf surfaces that contain chloroplasts (typically $6$ per cell) to regulate pore opening and gas exchange.

Epidermal cell

A cell that forms the protective outer tissue layer covering a leaf; typical leaf epidermal cells contain $0$ chloroplasts.

Diploid number of chromosomes

The condition of having two complete sets of chromosomes, found in somatic cells such as liver and muscle cells, but not in haploid gametes like sperm cells.

Trachea

The windpipe organ of the breathing system that channels air to the bronchi, whose luminal surface is lined with ciliated epithelial tissue.