Earlier this year, year 7 completed an investigation titled ‘To Float or Not to Float?’. They were experimenting to determine whether salt affects the ability for objects to float in water. Each group was provided with a golf ball (that sank in tap water), a beaker and some salt. Students added and dissolved salt into the water, which causes the density of water to increase. The golf ball was more dense than tap water and hence sunk in the water, however, the golf ball is less dense than very salty water and hence floats in salt water. Our groups found that 200 mLs of water needed on average around 10 large tea spoons of salt fully dissolved to cause the golf balls to float.
So what do you think, if we removed the salt from the ocean, would most boats sink?
Recently in year 8 we have been studying cells. While studying cells students have learned about all the tiny ‘organelles’ (little organs) inside the cell. An organelle of particular importance is the chloroplast. Chloroplasts absorb light and are the part of plant cells where photosynthesis occurs.
Photosynthesis is a vital chemical reaction that converts and stores energy from the sun into sugar (glucose). The reaction also removes Carbon Dioxide from the atmosphere and gives off Oxygen. The removal of Carbon Dioxide is vital for a healthy atmosphere – currently our society’s addiction to burning fossil fuels is building up significant levels of Carbon Dioxide in the atmosphere, which is slowly causing the Earth to get warmer. The addition of Oxygen is also vital as all living things (including plants) use Oxygen to extract energy stored in sugars through the chemical reaction called respiration (which some people refer to as the reverse reaction to photosynthesis).
It is important to remember that plant’s are living things as well. Viewing chloroplasts with a microscope is an easy way to remind students of this fact. One of the criteria used by year 8 to determine if something is living or not is whether it responds to changes in the environment. Chloroplasts are able to directly respond to changes in the amount of light available. In low light they have been seen to spread out, increasing their surface area to absorb the most light possible. In intense light, like the focussed light from the microscope lamp, the chloroplasts attempt to align themselves ‘edge on’ to the light and continually move seeking shelter behind other chloroplasts.
The video below was taken during class using a mobile phone camera held up just in front of the microscope lens (very fiddly, sorry for the unstable video!). If you’re able to see past the shaky filming you will see this amazing stimulus-response reaction from the chloroplast and see conclusive evidence that plants are living!
(if you’re struggling with the shaky film, skip forward to 0:46 seconds).
Or check out this more stable version from mantismundi user on youtube: