TOPIC 4

Cell wall

a freely permeable wall around plant cells, made mainly of cellulose.

Suberina

waterproof chemical that impregnates cellulose cell walls in cork tissues and makes them impermeable.

Lignin

a chemical that impregnates cellulose cell walls in wood and makes them impermeable.

Middle lamella

the first layer of the plant cell wall to be formed when a plant cell divides, made mainly of calcium pectate (pectin) that binds the layers of cellulose together.

Pectin

a polysaccharide that holds cell walls of neighboring plant cells together and is part of the structure of the primary cell wall.

Primary cell wall

the first very flexible plant cell walls to form, with all the cellulose microfibrils orientated in a similar direction.

Secondary cell wall

the older plant cell wall in which the cellulose microfibrils have built up at different angles to each other, making the cell wall more rigid.

Hemicelluloses

polysaccharides containing many different sugar monomers.

Plant fibers

long cells with cellulose cell walls that have been heavily lignified, so they are rigid and very strong.

Composite material

a material made of two or more materials which combined together make a composite with different properties from either of the constituent materials.

Turgid

swollen.

Flaccid

floppy, soft.

Plasmodesmata

cytoplasmic bridges between plant cells that allow communication between the cells.

Symplast

all of the material (cytoplasm, vacuole, etc.) contained within the surface membrane of a plant cell.

Pits

thin areas of cell wall in plant cells with secondary thickening, where plasmodesmata maintain contact with adjacent cells. In xylem vessels, where the cells are dead, they become simple holes through which water moves out into the surrounding cells.

Tonoplast

the specialized membrane that surrounds the permanent vacuole in plant cells and controls the movement of substances into and out of the cell sap.

Cell sap

the aqueous solution that fills the permanent vacuole.

Osmosis

a specialized form of diffusion that involves the movement of solvent molecules down their water potential gradient.

Chloroplasts

organelles adapted to carry out photosynthesis, containing the green pigment chlorophyll.

Chlorophyll

the green pigment that is largely responsible for trapping energy from light, making it available for the plant to use in photosynthesis.

Amyloplast

plant organelles that store starch.

Parenchyma

relatively unspecialized plant cells that act as packing in stems and roots to give support.

Collenchyma

plant cells with areas of cellulose thickening that give mechanical strength and support to the tissues.

Sclerenchyma

plant cells that have very thick lignified cell walls and an empty lumen with no living contents.

Sclereids

sclerenchyma cells that are completely impregnated with lignin.

Xylem

the main tissue transporting water and minerals around a plant.

Phloem

the main tissue transporting dissolved food around the plant.

Vascular bundle

part of the transport system of a plant, with phloem on the outside and xylem on the inside, often with strengthening sclerenchyma.

Cambium

the layer of unspecialized plant cells that divide to form both the xylem and the phloem.

Protoxylem

the first xylem that can stretch and grow.

Metaxylem

consists of mature xylem vessels made of lignified tissue.

Transpiration

the movement of water up from the soil, through the root hair cells, across the root to the xylem, then up the xylem, across the leaf, until it is lost by evaporation from the leaf cells, and diffuses out of the stomata down a concentration gradient.

Translocation

the active movement of substances around a plant in the phloem.

Sieve plates

the perforated walls between phloem cells that allow the phloem sap to flow.

Companion cells

very active cells closely associated with the sieve tube elements that supply the phloem vessels with everything they need and actively load sucrose into the phloem.

Tensile strength

the resistance of a material to breaking under tension.

Carbon neutral

a process where no net carbon is released into the atmosphere.

Bioplastics

plastics based on biological polymers.

Binary fission

asexual reproduction in bacteria in which the bacteria split in half.

Culture

growing microorganisms in the laboratory, providing them with the nutrients, oxygen, pH, and temperature they need to produce large numbers so they can be observed and measured.

Sterile

something free from living microorganisms and their spores.

Aseptic technique

a method for carrying out a procedure to prevent contamination by unwanted microorganisms.

Aspirin

a widely used drug that relieves pain and reduces blood clotting and inflammation.

Digitalis

a chemical found in foxgloves that affects the beating of the heart.

Oedema

swelling of the tissues due to fluid retention.

Digoxin

a drug based on the chemical found in foxgloves that improves heart function.

Placebo

an inactive substance resembling a drug being trialed, which is used as an experimental control.

Double-blind trial

a clinical drug trial where neither the doctor nor the patient knows whether the patient is receiving the new medicine, a control medicine, or a placebo.

Placebo effect

when patients appear to respond to a drug simply because they think it's doing them good.

Biodiversity

a measure of the variety of living organisms and their genetic differences.

Evolution

the process by which natural selection acts on variation to bring about adaptations and eventually speciation.

Taxonomy

the science of describing, classifying, and naming living organisms.

Morphology

the study of the form and structure of organisms.

Analogous features

features that look similar or have a similar function, but are not from the same biological origin.

Homologous structures

structures that genuinely show common ancestry.

Domains

the three largest classification categories

Kingdom

the classification category smaller than domains; there are six kingdoms

Phylum (division, for plants)

a group of classes that all share common characteristics.

Class

a group of orders that all share common characteristics.

Order

a group of families that all share common characteristics.

Family

a group of genera that all share common characteristics.

Genus

a group of species that all share common characteristics.

Species

a group of closely related organisms that are all potentially capable of interbreeding to produce fertile offspring.

Archaea

domain made up of bacteria-like prokaryotic organisms found in many places, including extreme conditions and the soil; they are thought to be early relatives of the eukaryotes.

Archaebacteria

ancient types of bacteria found in many different environments.

Eubacteria

true bacteria (prokaryotic organisms).

Protista

a kingdom in the five-kingdom classification system that contains all single-celled organisms, green and brown algae, and slime molds.

Fungi

eukaryotic kingdom of heterotrophs with chitin in their cell walls.

Plantae

mainly autotrophic eukaryotic kingdom containing mosses, liverworts, ferns, gymnosperms, and angiosperms (the flowering plants).

Animalia

a mainly heterotrophic eukaryotic kingdom including all the invertebrates and vertebrates.

Morphological species model

a species definition based solely on the appearance of the organisms observed.

Sexual dimorphism

describes species where there is a great deal of difference between the appearance of the male and female.

Molecular phylogeny

the analysis of the genetic material of organisms to establish their evolutionary relationships.

Ecological species model

a species definition based on the ecological niche occupied by an organism.

Mate-recognition species model

a species definition based on unique fertilization systems, including mating behavior.

Gazelle species model

a species model based on DNA evidence.

DNA sequencing

the process by which the base sequences of all or part of the genome of an organism are worked out.

DNA profiling

the process by which the non-coding areas of DNA are analyzed to identify patterns.

Gel electrophoresis

a method of separating segments of proteins or nucleic acids based on their electrical charge and size.

Extremophiles

bacteria that can survive extreme conditions of heat, cold, pH, salinity, and pressure.

Phylogenetic tree

a model used to show the relationships between different groups of organisms.

Endosymbionts

organisms that live inside the cells or the body of another organism.

Monera

a kingdom in the five-kingdom classification system that contains the Archaea and Eubacteria.

Ecosystems

biological communities where organisms interact with one another and with their physical environment.

Species richness

the number of different species in an area.

Relative species abundance

the relative numbers of species in an area.

Biodiversity hotspot

an area with a particularly high level of biodiversity.

Endemic

a species that evolves in geographic isolation and is found in only one place.