The 2nd chapter of the Singapore GCE O Level syllabus is all about substances moving across membranes, with or without the expenditure of energy, up or down a concentration gradient, with or without a partially permeable membrane. So which is which?

Diffusion

• Movement of any particles
• Down a concentration gradient (higher to lower concentration)
• Without expenditure of energy
• Does not require a partially permeable membrane

Osmosis

• Movement of water molecules
• From a region of higher water potential to a region of lower water potential
• Without expenditure of energy
• Requires a partially permeable membrane

Active transport

• Movement of particles (usually ions)
• Against a concentration gradient (lower to higher concentration)
• With expenditure of energy

Hope this sums up the basic concepts for you!

In the spirit of World Cup fever, I was telling my Friday Sec 4 Bio class about Paul the Psychic Octopus which predicts the outcomes of football matches. One of my students asked what is the difference between a squid and an octopus, so I drew this cartoon to explain.

Learn the differences

1. A squid is made into calamari while an octopus is made into takopachi.
2. A squid is pointy while an octopus is more rounded and blobby.
3. Squids move by ejecting jets of water out of their body while octopuses use their tentacles to glide across the ocean floor.
4. Squidward Tentacles from Spongebob Squarepants is actually an octopus.

See, learning Biology with me is never boring and usually quite entertaining!

Cell Structure and Organisation is the first chapter you will learn in O Level Biology. It’s quite a simple chapter, you will learn about plant cells, animal cells, and three kinds of specialised cells – xylem vessels, root hair cells and red blood cells.

The questions comparing plant cells and animal cells are quite repetitive, it should be no problem to remember that the three main differences are chloroplasts, cell wall and sap vacuole, all of which are present in plant cells but not in animal cells.

When it comes to naming organelles in animal cells, note that it is one “mitochondrion” and many “mitochondria”. Mitochondria is plural!

Xylem vessels, root hair cells and red blood cells are all involved in transport of substances. However, they have different adaptations which affect how they carry out their functions. A xylem vessel’s job is to carry water up the plant, as quickly as possible. Hence it is a long, hollow tube to reduce resistance to water flow, and it is strengthened by lignin so that it can withstand the high pressures of water flowing through.

Root hair cells are long and narrow to increase the surface area, so that they can absorb water and mineral ions from the soil as efficiently as possible. As water enters by osmosis, the concentration gradient between the cell and soil water must be as steep as possible. To facilitate this, the root hair cell has a vacuole filled with concentrated cell sap so that water will enter the cell by osmosis.

Red blood cells are biconcave to increase their surface area so that diffusion of oxygen can happen faster. They also have no nuclei, so that there can be more space for haemoglobin molecules which are required for oxygen transport. Finally, they’re bendy! They’re flexible so that they can squeeze through narrow blood capillaries by becoming bell-shaped. Isn’t that cute?

Finally, you are required to know that cells make tissues, which make organs. Several organs working together will form an organ system, for example the digestive system. Finally, an organism is made up of many different organ systems.

Biology classes for Sec 3 and Sec 4 students have been confirmed! Below is the schedule:

Sec 4 Pure Biology: Monday 7-9pm, Friday 7-9pm (choose one slot)

Sec 4 Combined Science: Sunday 2-4pm

Sec 3 Pure Biology: Wednesday 7-9pm

Sec 3 Combined Science: Sunday 4-6pm

For a free consultation session with me, please call 65-62513359 to book an appointment! Our office is located at 273 Thomson Road, across the road from Novena MRT and Novena Church.

Hello students! In the June holidays I will be running an O Level Revision Series for Biology.

Find out how you can make studying Biology easy, efficient and enjoyable with these Power-Up Tips!

I will be having a workshop on Saturday, 20th March 2010. This workshop will cover certain skills that will make learning Biology much easier and so much more intuitive. Call now to attend our free preview at 7.30pm on the 18th of March 2010.