Practical - Is It Alive? Part 1 and 2 - 27 June 2012

List all the characteristics of living things.

All living things…

·        have the ability to reproduce

·        can move

·        can grow

·        will die

·        respond to changes

·        are made of cells

·        have hereditary information

·        can egest waste

·        can respire

·        have the ability to evolve 

  Scientific terms:

1.     Excretion: The process, act or function of discharging or ejecting waste product of metabolism, especially from the system of an organism. Examples of excreta: liquid waste like urine and sweat

2.     Egestion: Egestion is the discharge or expulsion of undigested material (food) from a cell in case of unicellular organisms, and from the digestive tract via the anus in the case of multicellular organisms. (Releasing faeces)                                                                                  [Definitions taken from Biology online Dictionary]

Note: Do not get confused with excretion and egestion!

List all the characteristics needed to support life

  All living things…

·      need air to survive

·      need water to survive

·      need food to survive (eg. Plants need light to photosynthesise to grow and survive)

·      need shelter to survive

·      can adapt to changes to survive

·      plants need warmth to survive

Suppose you are given some unknown pellets. How are you going to carry out experiments to find out are the unknown substances living things?

  Using the knowledge of “all living things can move” and “all living things are made out of cells”, we can examine the substances under a microscope and at the same time, we can observe and take note of their behaviour and movement. Therefore, if the substances contain cells and are able to move, they are living things.

Three different types of liquids – water, glucose and salt water are also provided to test the reactions of the substance to these liquids.

Why were these liquids chosen?

Living things are made up of cells. When cells are immersed in glucose solution, the cells will increase in size as the water molecules from the glucose solution are small enough to pass through the cell membrane. Moreover, the glucose solution is a source of food for the living substances. When the cells are immersed in salt solution, the cells will decrease in size due to the movement of water in the cell out of the cell to the salt solution. The molecules in the salt solution are not able to enter the cell as they are too large to pass through the cell membrane. Therefore, we can determine that the substances are living things by placing them in the different solutions and observing them to see if their reaction is the same as a typical cell.

Part 1 

 

Table 1: Observation of substances A, B, C, D and E in water





  Photo: Observation of substances A, B, C, D and E in water after 10 minutes.