Levels of Organisation within Organisms

The basic building block of life is the cell, which is termed the first level of organisation.
Cells that carry out similar functions group together to form tissues. For example, muscle tissue, nervous tissue, and connective tissue.
Various tissues further combine, creating the next level of organisation, i.e., organs. They perform specific functions. Examples include the heart, lungs, stomach, and brain.
Different organs collaborate to form organ systems, such as the circulatory system, digestive system, and nervous system. Organ systems work together to maintain overall body function.
The highest level of organisation is the organism itself - an individual being that can carry out all basic life processes. This could be a human, a dog, a fish, or a tree.
Together, all these levels combine to create the complex internal structure of all living organisms, from unicellular bacteria to large multicellular organisms like humans and elephants.

Now, highlighting some key points on “Movement Across Membranes”:

Cellular membranes are semi-permeable, meaning they allow some substances to pass through while blocking others.
Movement across membranes is crucial for the functioning of cells. It can happen in various ways such as diffusion, osmosis, and active transport.
Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration.
Osmosis is a specific type of diffusion involving water molecules. It occurs from a region of high water concentration to a region of low water concentration through a partially permeable membrane.
Active transport is the movement of molecules against their concentration gradient (from low to high concentration). It requires energy in the form of ATP (adenosine triphosphate) to occur.
Facilitated diffusion is a process where substances move down their concentration gradient with the help of transport proteins in the cell membrane.
These processes are vital for the exchange of nutrients and waste between the cell and its environment, maintaining cell homeostasis.