FACT
ATP and ADP are
molecules involved
with moving energy
within cells. You do
not need to know
these names in full
and will learn more
about them later.Figure 3.18: Facilitated diffusion in cell membrane, showing ion channels and carrier proteins.Examples of substances moved via facilitated diffusion include all polar molecules such as
glucose or amino acids.
- Active transport
Active transport is the movement of substancesagainsta concentration gradient, from a
region oflow concentrationtohigh concentrationusing an input of energy. In biological
systems, the form in which this energy occurs isadenosine triphosphate (ATP). The process
transports substances through a membrane protein. The movement of substances is selective
via the carrier proteins and can occur into or out of the cell.
Figure 3.19: The sodium-potassium pump is an example of primary active transport.Examples of substances moved include sodium and potassium ions as shown in Figure 3.19
3.4 Cell organelles
We will now look at the key organelles that make up the cell. It is important to bear in mind
that structure and function are closely related in all living systems. When studying each
organelle, ensure that you observe the specific structures (from micrographs) that allow the
organelle to perform its specific function.
Cytoplasm DUMMY
The cytoplasm is the jelly-like substance that fills the cell. It consists of up to 90% water. It
also contains dissolved nutrients and waste products. Its main function is to hold together
Chapter 3. The basic units of life 79