IB DP Biology SL 2025 - Unity and diversity: Molecules & Cells

Polar Covalent

Unequal sharing of electrons

Hydrogen bonds

Very weak bonds; occurs when a hydrogen atom in one molecule is attracted to the electrostatic atom in another molecule

Adhesion

An attraction between molecules of different substances

Cohesion

Attraction between molecules of the same substance

Hydrophilic

Attracted to water

Hydrophobic

Water hating, non-polar

Buoyancy

The ability or tendency to float in water or air or some other fluid.

Viscosity

A liquid's resistance to flowing

Thermal conductivity

The ability of an object to transfer heat

Specific heat capacity

The amount of heat energy required to raise the temperature of one gram of substance by one degree celsius

Metabolism

All of the chemical reactions that occur within an organism

Electronegativity

A measure of the ability of an atom in a chemical compound to attract electrons

Polarity

Molecules having uneven distribution of charges

Solvent

A liquid substance capable of dissolving other substances

DNA

Material present in nearly all living organisms as the main constituent of chromosomes. It is the carrier of genetic information.

RNA

Single-stranded nucleic acid that contains the sugar ribose

Double stranded

Structure of DNA

Nucleotides

Basic units of DNA molecule, composed of a sugar, a phosphate, and one of 4 DNA bases

Pentose sugar

A five-carbon sugar molecule found in nucleic acids

Nitrogenous bases

Adenine, guanine, cytosine, thymine, uracail

Phosphate group

A chemical group consisting of a phosphorus atom bonded to four oxygen atoms; important in energy transfer.

Gene expression

Process by which a gene produces its product and the product carries out its function

Adenine and guanine

Nitrogenous bases in DNA

Cytosine and thymine

Nitrogenous bases in DNA

Uracil and cytosine

Nitrogenous bases in RNA

Ribose

A five-carbon sugar present in RNA

Deoxyribose

A five-carbon sugar that is a component of DNA nucleotides

Base paring

Nitrogen bases only line up with certain nitrogen bases

Nucleus

Control center of the cell

Vacoule

An organelle that stores water, food or other substances; plant cells have a large central vacoule

Plasmid

A small ring of DNA that carries accessory genes separate from those of the bacterial chromosome

Cell wall

A rigid structure that surrounds the cell membrane and provides support to the cell

Cell membrane

A cell structure that controls which substances can enter or leave the cell.

Ribosomes

Protein synthesis

Capsule

A sticky layer that surrounds the cell walls of some bacteria, protecting the cell surface and sometimes helping to glue the cell to surfaces.

Flagella

Whiplike tails found in one-celled organisms to aid in movement

Pili

Short, hairlike protein structures on the surface of some bacteria

Mitochondria

Powerhouse of the cell

Cell theory

Idea that all living things are composed of cells, cells are the basic units of structure and function in living things, and new cells are produced from existing cells

light microscope

Microscope that uses a beam of light passing through one or more lenses to magnify an object

electron microscope

Microscope that forms an image by focusing beams of electrons onto a specimen

Advantages of light microscope

Able to view living organisms, relatively inexpensive

Disadvantages of light microscope

Limited magnification and resolution

Advantages of electron microscope

High resolution, good magnification, different computer viewing capabilities (3D, interior etc)

Disadvantages of electron microscopes

Cannot view living specimens, expensive

Specimen

Sample

Resolution of a microscope

The sharpness or clarity of an image.

Magnification

The ratio of an object's image size to its real size

Freeze fracture microscopy

Cells are frozen and then a knife is used to crack them open. The crack often passes through the interior of cell and internal membranes. The "bumps" that appear are usually large proteins or aggregates embedded in the interior of the membrane.

Cryogenic electron microscopy

A technique in which samples are frozen to cryogenic temperatures, then viewed using electron microscopy.

Immunofluorescence

Method of tagging antibodies with a luminating dye to detect antigen-antibody complexes

Fluorescent dyes

Staining technique using special microscopes that detect chemical fluorescence due to special stains

Prokaryotic

cells that do not have a nucleus

Eukaryotic

A cell characterized by the presence of a nucleus and other membrane-bound organelles. Eukaryotes can be unicellular (protists) or multicellular (fungi, plants and animals).

Plasma membrane

A selectively-permeable phospholipid bilayer forming the boundary of the cells

Unicellular

Made of a single cell

Multicellular

Consisting of many cells

Naked DNA in loop

Not associated with histone proteins (as it is in eukaryotic cells)

Compartmentalisation

The formation of separate membrane-bound areas in a cell

Smooth endoplasmic reticulum

Produces and stores lipids, including steroids.

Rough endoplasmic reticulum

Has ribosomes attached to its surface which produce proteins that are usually destined for use outside the cell.

Golgi Apparatus

Processes and packages proteins, which are then released in Golgi vesicles.

Vesicle

Small sac that transports and releases substances produced within the cell by fusing with the cell membrane.

Cytoskeleton

A system of protein fibres called microtubules and microfilaments. The cytoskeleton helps to hold organelles in place and maintain the structure and shape of the cell.

Archea

Domain of unicellular prokaryotes that have cell walls that do not contain peptidoglycan