Variation means difference in genetic makeup between individuals within a specie.
<u>Answer</u>:- Active transport
<u>Explanation</u>:-
There are two types of membrane transports
1. Passive transport - this type of transport occurs without the input of any energy and the molecules move along the concentration gradients that is from <em>high concetration to low concentration.</em>
2. Active transport- this type of transport takes place to move the molecules against the concentration gradient that is from <em>low concentration to high concentration.</em>
<em>The active transport is of two types:</em>
1. <em>Primary active transport-</em> in this type of transport <em>ATP</em> is used as an energy source to move the substances against the concentration gradient.
2.<em>Secondary active transport</em> - in this type of transport the gradient formed by the active transport is utilized and it involves the movement of 2 substances at a time aross the membrane. That is the movement of one molecule is coupled to another.
- The membrane proteins that are associated with active transport are called as <em>carrier proteins</em>. These proteins have a binding site for the molecules that they transport. Once they bind to the specific molecules, a conformation change is induced and this leads to the transport of the molecule across the membrane.
So, the <em>active transport is basically responsible for utilizing the energy from ATP and carrier proteins to move the substances across the membrane against their concentration gradient i.e. from low concentration to high concentration.</em>
The flow of energy in an ecosystem is best described as energy moving in one direction from the sun to the producers then to the consumers.
Explanation;
Energy flow is the amount of energy that moves through successive trophic levels of a food chain in an ecosystem. Ecosystem maintain themselves by cycling energy and nutrients.
The energy from sunlight is taken up by producers which use it to produce organic compounds through photosynthesis. The energy is then passed successively to the trophic levels, that is from the producers to the consumers ( primary, secondary, tertiary and quotienary consumers). During this transfer some energy is lost at each trophic level in form of heat.
