DP Biology Unit 1: Life under the microscope - Core

covalent bond

A chemical bond between two atoms formed by sharing electrons

electronegativity

A measure of how much an atomic nucleus attracts the electrons that are involved in a chemical bond

polar

Molecules in which there are positive and negative areas of electrostatic charge.

hydrogen bond

A weak intermolecular force that exists when electronegativity creates a polar covalent bond.

cohesion

The force of attraction between the molecules of the same substance

adhesion

The force of attraction between different types of molecules or substances

solvent

The medium into which solutes will dissolve through solvation

capillary action

The ability of a liquid to move through narrow tubes that results from cohesion, adhesion and surface tension

hydrophilic

The property of polar substances that attract water molecules

hydrophobic

The property of non-polar substances that repel water molecules

amphipathic

A molecule or compound that has both hydrophobic (water-repelling) and hydrophilic (water-attracting) properties

buoyancy

An upward force on an object in a fluid that opposes the weight (gravitational force)

vicosity

The property of a fluid related to its resistance to flow

thermal conductivity

The property of a substance to transfer heat energy

specific heat capacity

The quantity of energy required to change the temperature of a given amount of a substance

cell theory

All living things are made of individual units, cells, which are the basic units of life, and that all cells arise from other cells

light microscope

A microscope that uses light to view specimens, usually with a magnification of 400-1500 times

spontaneous generation

A now disproved theory that living organisms could arise from non-living matter, such as soil, manure and decaying corpses

deductive reasoning

Drawing a logical conclusion from the evidence presented

electron microscope

Instrument using a beam of electrons to obtain a magnified image of a very small object such as a sub-cellular structure

stains

A chemical solution that is applied to a sample being viewed under a microscope to increase the contrast between different areas on the sample to make them more visible

eyepiece graticule

A transparent ruler that is placed in the eyepiece lens of a light microscope to measure the actual size of objects in the image

stage micrometre

Small, calibrated rulers that are mounted onto the stage of a microscope and allow precise measurements of distance

resolution

The shortest distance between two separate points in a microscope's field of view that can still be distinguished as separate objects.

SEM image

Creates an image by detecting reflected or knocked-off electrons

TEM image

Creates an image from transmitted electrons (electrons that are passing through the sample)

freeze fracture microscopy

A technique to visualise structures of biological samples which have been frozen then broken into small pieces

cryogenic electron microscopy

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

immunofluorescence

A technique in which a fluorescent tag is attached to antibodies, which bind to antigens on a structure being viewed allowing visualisation of location of target molecules

prokaryotic/prokaryotes

A group of organisms whose cells do not contain a proper nucleus (enclosing their genetic material) or membrane-bound organelles

eukaryotic/eukaryotes

A group of organisms whose cells typically contain a true nucleus (enclosing their genetic material) and membrane-bound organelles

organelles

Specialised structures inside cells with specific functions (and usually membrane bound, but not always eg ribosomes)

ribosomes

Subcellular structures (organelles) in which protein synthesis takes place (70S in prokaryotyes & 80S in eukaryotes)

archaea

Single-celled microorganisms that are similar to, but evolutionarily distinct from bacteria

ultracentrifuges

A laboratory instrument that uses centrifugal force, generated through spinning, to separate molecules of different sizes and densities in a sample

compartmentalisation

The organisation of different functions and processes within specific subcellular structures separated by plasma membranes

plasma membranes

A thin, selectively permeable layer of phospholipid and protein molecules that surrounds the cell, acting as a boundary and regulating the passage of molecules and ions in and out of the cell

cell wall (prokaryotic)

Consists of peptidoglycan, provides shape and allows the cell to withstand turgor pressure without bursting

cell wall (eukaryotic)

If present, consists of cellulose or possibly chitin

DNA (prokaryotic)

A single loop of DNA, referred to as 'naked' due to it not being assocaited with histone proteins, stores the information necessary for synthesising proteins

nucleoid

An irregularly shaped region within the prokaryotic cell that contains all or most of the genetic material

plasmid*

Small circular DNA molecule, also 'naked', physically separate from and replicates independently of the nucleoid DNA. Can be shared between bacteria and often contain genes for antibiotic resistance (*Structure is found in SOME but not ALL prokaryotic cells).

capsule*

Helps the cell keep from dehydrating and adhere to surfaces (*Structure is found in SOME but not ALL prokaryotic cells).

flagellum*

A hair-like appendage that protrudes from certain cells, and from a wide range of microorganisms to provide motility (*Structure is found in SOME but not ALL prokaryotic cells).

pilli*

Protein filaments on the cell wall that help with cell adhesion and transferring of DNA between two cells (*Structure is found in SOME but not ALL prokaryotic cells).

cytoplasm (prokaryotic)

water-based jelly-like fluid that fills the cell, suspends ions, organic molecules, DNA and ribosomes, and is the site of metabolic reactions

cytoplasm (eukaryotic)

Gel-like substance that fills the interior of cells, consisting of organelles, cytoskeleton and other structures

mitochondria

Double-membrane-bound organelles that convert glucose into ATP

nucleus

A double membrane-bound organelle that contains the genetic material (DNA) of eukaryotic cells

histone proteins

Proteins around which eukaryotic DNA is wrapped, forming structures called nucleosomes. This organisation helps to regulate gene expression and protect the structural integrity of DNA

Golgi apparatus

A membrane-bound organelle that sorts, modifies and packages proteins and lipids for transport to other parts of the cell or for secretion out of the cell

lysosomes

Compartmentalised spaces within cells that are responsible for breaking down and recycling waste materials

phagocytic vacuoles

Similar to lysosomes and used by macrophages to break down pathogens into parts, which can then be used to develop an immune response

cytoskeleton

A network of protein fibres that provides shape and allows for the movement of molecules around the cell

vesicle

Small, membrane-bound sacs within the cell that transport and store various molecules

vacuole

Membrane-bound organelle that helps to maintain the osmotic balance of the cell

rough endoplasmic reticulum

A network of membranes within the cell that is studded with ribosomes, which are responsible for synthesising proteins

smooth endoplasmic reticulum

Meshwork of fine disk-like tubular membrane vesicles, part of a continuous membrane organelle within the cytoplasm of eukaryotic cells

DNA (eukaryotic)

Deoxyribonucleic acid, contained in the cell's nucleus, the molecule that carries genetic information for development and functioning of an organism

atypical cells

examples include aseptate fungal hyphae, skeletal muscle, red blood cells and phloem sieve tube elements as they are either multinucleate or anucleate

anucleate

A eukaryotic cell without a nucleus

multinucleate

A cell containing more than one nucleus

transcription

Process by which the genetic information encoded in DNA is copied into RNA

mRNA

Messenger RNA, a type of RNA that carries the genetic information from DNA in the nucleus to ribosomes in the cytoplasm, where it is used as a template to synthesise proteins

translation

Process by which ribosomes use the genetic information carried by mRNA to synthesise proteins

post-transcriptional modification

Changes to mRNA after transcription, including removal of pieces of the mRNA and other modifications that are necessary for a working protein to be produced

extracellular signal

A signal from outside the cell, such as a hormone or growth factor, that can affect the cell's behaviour

Induced pluripotent stem cells (iPS) cells

These are cells that have been reprogrammed to have the ability to generate many different cell types

zygote

A fertilised egg

gamete

A reproductive cell of an animal or plant

morula

Solid ball of cells formed from divisions of the zygote

blastocyst

A cluster of dividing cells formed by the fertilised egg during early embryonic development

trophoblast

Cells that will become the placenta

inner cell mass (ICM)

Cells within the blastocyst that will become the embryo

differentiation

The process by which cells become specialised to carry out specific functions

undifferentiated

A cell that does not have the specific structural or functional characteristics of any mature cell type

specialised cells

Cells with specific functions or structures that are different to other cells and have specific roles or tasks

morphogens

A chemical in the cell the concentration gradient of which determines the fate of surrounding cells

totipotent stem cells

Cells that have the ability to divide to generate the entire organism and can differentiate into any type of cell including placental cells (e.g. the eight cells of the morula)

pluripotent stem cells

Can differentiate into all body cells, but cannot give rise to a whole organism (e.g. embryonic stem cells of the blastocyst)

multipotent stem cells

Cells that can generate many cells of an organism and differentiate into a few closely related types of body cell (e.g. umbilical cord stem cells)

unipotent stem cells

Cells that can generate one cell type of an organism and can only differentiate into their associated cell type (e.g. liver stem cells can only make liver cells)

stem cell harvesting

(umbilical) cord blood is rich in stem cells, which can be harvested at birth and potentially used to treat many different cancers, immune deficiencies and genetic disorders

stem cell niche

The microenvironment within the organism in which the stem cells exist and receive their instructions

signalling molecules

Substances that can activate, or prevent genes from transcribing, lleading to some cells being instructed to remain dormant (inactive) while others are directed to make more of the same kind of stem cell. Still others become differentiated into another kind of cell.

haematopoietic

Immature stem cells that form blood cells

bone marrow

The soft, spongy centre of most bones and has many blood vessels associated with it and source of blood stem cells throughout adulthood

bulge stem cells

Found in the bulge of a hair follicle responsible for generating and maintaining a constant covering of body hair

size differential

The volume inside a human egg cell is about 10 million times larger than the volume of a sperm cell - the egg cell is one of the largest in the human body, while the sperm cell is one of the smallest

sciatic nerve

Contains the longest neurones in the body with axons that can exceed 1 m (from base of the spine to the foot)

erythrocytes

The proper name for red blood cells which are some of the smallest cells in the human body (7.5 µm) and have no nucleus, leaving space for more haemoglobin and a biconcave shape with a highly flexible membrane that allows them to be repeatedly deformed and spring back in shape

leukocytes/leucocytes

White blood cells form part of the immune system involved in protecting the body against infectious diseases and foreign invaders. Less common and larger than rbcs, they have nuclei (unlike rbcs), there are many different types of white blood cells that vary in size (10 to 20 µm), structure and function

surface area:volume (SA:V)

the volume of a cell increases at a greater rate (cubed) than the surface area (squared), consequently the larger a cell becomes, the more the SA:V ratio reduces

plastid

Small organelles responsible for manufacturing and storing chemical energy (eg chloroplasts)

metabolism

Chemical reactions that take place within the cell(s) of an organism

response to stimuli

Responding to changes in the external environment

homeostasis

The maintenance of constant internal conditions, despite changes in their external environments

movement

Having some control over their place and position

growth

Increasing in size over a period of time. In multicellular organisms, growth can also refer to an increase in the number of cells that make up an organism

reproduction

The production of offspring