Define the following terms

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Holozoic is a type of nutrition which concerns humans and other mammals. Food is taken into the digestion system and broken down, and the useful products absorbed. There is a great variety of feeding mechanisms among holozoic animals. Methods of feeding have been classified on the relative size of food particles ingested. See the table below for classification:

Feeding by intake of small particles

Feeding by intake of fluid food or soft tissue

Feeding by intake of large particles

Microphagous feeders

Fluid feeders

Macrophagous feeders

So it basically means, feeding like an animal, taking organic matter in and digesting it into a form suitable for absorption, e.g. human nutrition.


Also known as autotrophic (‘self nourishing’), most plants are autotrophs hence they make their own organic nutrients (food) from an external supply of relatively simple raw materials (in organic nutrients), using energy from sunlight in photosynthesis. Autotrophs go onto make all their other requirements from the products of photosynthesis by combining them with each other and with additional inorganic nutrients.

Holophytic or autotrophic is the form of nutrition of green plants, algae and photosynthetic bacteria (cyanobacteria).

Antagonistic muscles

All muscles work in pairs. Whether they are striped muscle, smooth muscle or cardiac muscle makes no difference, all muscles must work in pairs. This is because they can contract and relax but cannot push or stretch themselves. Antagonistic muscles are pairs of muscles that work against each other. One muscle contracts (agonist, or prime mover) while the other one relaxes (antagonist) and vice versa.

When your biceps contracts it flexes (bends) the elbow joint. At the same time it also pulls the triceps to make it longer. So the triceps is stretched by the biceps pulling it. When the triceps contracts is extends (straightens) the elbow joint, and at the same time it pulls the biceps and makes it longer. So these two muscles work together. Neither muscle can stretch itself, it must be stretched by its antagonist (partner).

Anaerobic respiration

Reactions of respiration inside cells are known as tissue respiration and they are dependent up gaseous exchange between the organism and the environment. Most respiration requires oxygen and is known as aerobic respiration, the end products are carbon dioxide and water (e.g. respiration in plants, glucose + oxygen ==> carbon dioxide + water).

Respiration can also take place in the absence of air (oxygen), this is called Anaerobic respiration. This takes place in cells which are deprived of air, in order to maintain the supply of energy. In lactic acid formation, the sole waste product is lactic acid. Vertebrate skeletal (e.g. mammals) muscle tissue may respire anaerobically, forming lactic acid:

Glucose –> lactic acid + Energy

C6 H12 O6 –> CH3 CH OH CO OH + Energy

Organisms that only respire in the absence of oxygen are also known as obligate anaerobes.

Natural selection

Is the process by which those organisms which appear physically, physiologically better adapted to the environment and have characteristics that give them a competitive advantage, survive and reproduce; those organisms not so well adapted either fail to reproduce or die.

There are many types of natural selection such as:

* Stabilising selection

* Directional selection

* Disruptive selection

Basically, natural selection operates in populations in nature. It is a process that brings about adaptation and evolution. Through uneven rates of reproduction the gene frequencies of populations are changed. E.g. If an animal or plant does not operate as effectively as others of the same species in the environment, then it will have less chance to perpetuate its genes through reproduction. Thus, natural selection brings about adaptation to environment.

Industrial melanism

Since the Industrial Revolution in the early part of the nineteenth century, air pollution by gases (sulphur dioxide) and solid matter (mainly soot) was distributed over the industrial towns and cities and the surrounding country side. The lichens and mosses on brickwork and tree trunks were killed off and the surfaces were blackened.

During this period, the amount of dark variety species of moth increased in these habitats as they were more camouflaged thus there is an increase in the frequency of their genes being past forward to the next generation because they survive. This rise in the proportion of darkened forms is known as industrial melanism. Read about cellular respiration breaking down energy


Osmosis in living organisms is the diffusion of water molecules across a selectively permeable membrane:

* From where water molecules are at a higher concentration to where they are at a lower concentration

* From a lower concentrated solution to a higher concentrated solution

* From a hypotonic solution to a hypertonic solution

* From a hyperosmotic solution to a hypo-osmotic solution

* From an area of high water potential to lower water potential

The diagram below shows a model of osmosis:

Active transport

In active transport molecules move from where they are in lower concentration where they are in higher concentration. A protein carrier molecule is used (Biological pumps). This is against the concentration gradient and always needs energy.

A plant may contain a higher concentration of Mg2+ ions than the soil. It obtains a supply by active transport through the cell surface membranes of the root hairs. Only Mg2+ ions can bind with the specific protein carrier molecules responsible for their entry into the plant. This is also known as active ion uptake, but it is a form of active transport.

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