1P13: Who Wrote the Secret Message?
In this lesson, we were required to detect the colour components of the black ink in the secret message. The aim of the activity is to use paper chromatography to find out which suspect wrote the secret message. We had to test different brands of black ink, brand A, B and C, and see which brand matched the one used in the secret message.
I learnt that in chromatography, when marking the ink spot on the paper, the ink spot should not touch the solvent when placed in the solvent as this would cause the ink spot to dissolve in the liquid solvent thus contaminating the chromatogram. Also, a pencil should be used to mark the starting line because if ink were to be used, it would dissolve into its various components and interfere with the experiment. I like the part where the ink spreads out into different colours. The sight is just so amazing. I do not really like the waiting part. We had to wait for quite long for the ink colours to spread out.
1P14: Inside of Cells
In this lab lesson, we examined an animal cell and a plant cell under a microscope and compared their differences. The aim of the activity was to observe the differences between animal cells (cheek cells) and plant cells (onion cells). Firstly, we added a drop of iodine onto the slide for both tests to stain the cells to give a constrasting view. We noticed a few differences, the plant cell has larger and fewer vacuoles but an animal cell has numerous and small vacuoles. Also, a plant cell contains a cell wall and starch grains but an animal cell does not have a cell wall or starch grains.
1P15: Bouncy Raw Egg with Moving Waters
In this lab session, we conducted 2 activities. Part 1 was the bouncy raw egg. We were supposed to put a quail egg in hydrochloric acid and observe its changes. However, this part was time consuming as we had to wait a few days before we get the desired results. The aim of this part was to demonstrate osmosis in living cells.
The 2nd part of the practical session is Moving Waters. Due to time constraint, this was a teacher's demonstration and we could not really take pictures. Here's a picture I got from the internet. The aim of this part is to demonstrate the process of osmosis. Firstly, the teacher told us and explained to us why the observations made are so and etc after the experiment.
I learnt that osmosis is essential living things. Without osmosis, living things would die. The cell membrane of the cells in living things are selectively permeable and only allows some substances to pass through but not others. Osmosis is the process whereby water moves from a region of less negative water potential to a region of more negative water potential across a selectively permeable cell membrane. Water enters and leaves living cells through their cell membrane by osmosis. I like the part 1 where the egg shell dissolves and the end result. The egg becomes bouncy. :) The worst part is that in part 2, we did not get to do the experiments ourselves. :(
1P16: The Riddle of the Poisoned Well
In this practical session, we are given a situation and we have to find a solution to the problem. The aim of this activity was to solve the riddle of the poisoned well. This was quite an interesting activity. This practical also involved osmosis.
I learnt that osmosis can change the shape of some objects. When the potato chip was placed in the Southern Well, the water potential inside the potato cell was less negative than that outside the cells due to the higher concentration of solutes present in the poisoned water. Hence, osmosis occurred and water molecules moved out of the potato cells down a water potential gradient via the selectively permeable membrane. The vacuole in each cell shrink and the cell membrane is pulled away from the cell wall, causing the cell to lose turgidity, thus decreasing in length. I liked the part when changes occurred and the worst part was the waiting.
1P17: Extracting Chlorophyll
In this practical session, due to undesired results again and again, our science teacher decided not to conduct this experiment anymore as he thought it was a waste of resources. The aim of this lab session was to extract chlorophyll from leaves. I learnt that chlorophyll is normally found on the green parts of the leaf. Starch is present on the green parts of the leaf but not on the yellow/white parts of the leaf. Chlorophyll is essential for plants as it uses it to photosynthesise and make food for the plant to survive. Furthermore, plants need chlorophyll so that they can produce not only glucose for themselves, but also oxygen for us, humans to breathe in to survive. There are many factors needed for photosynthesis to occur.
1P18: Artificial Intestines
In this practical session, we were required to observe the behaviour of the small intestine by making an artificial one. We firstly prepared the Visking tubing and the other apparatus needed. The aim of this experiment was to investigate the reason why food needs to be digested. I learnt that the iodine solution remains yellow-brown in the sample showing that there is no presence of starch. However, a brick red precipitate is formed when the sample is heated with Benedict's solution showing that there is a presence of reducing sugars (e.g. glucose). This is because the glucose molecules are small enough to diffuse across the selectively permeable membrane (Visking tubing) while the starch molecules are too large to diffuse through. This shows the importance of digestion in breaking down large complex molecules to smaller diffusable substances that can be absorbed into the bloodstream. I like the part when the change occured as it was very exciting. The worst part was the setting up of the experiment as my partner and I just could not set up the experiment properly.
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