The vasovagal syncope trigger causes your heart rate and blood pressure to drop suddenly. That leads to reduced blood flow to your brain, causing you to briefly lose consciousness.

Another requirement is a concentration difference, also referred to as the concentration gradient, which pertains to the difference in concentration between two areas. The movement of molecules will continue between the two areas as long as there is a concentration gradient.

In a cell, water, oxygen and carbon dioxide molecules can pass directly through the cell membrane without requiring any energy along the concentration gradient.

Facilitated diffusion is the diffusion process used for those substances that cannot cross the lipid bilayer due to their size. 

Facilitated diffusion is the process of moving molecules from high to low concentration across a membrane by using a protein channel in the membrane. Facilitated diffusion does not use energy but it relies on a protein to facilitate movement. So it consider a passive movement. 

Glucose & Amino acid 

Semi-permeable membranes are very thin layers of material which allow some things to pass through them, but prevent other things from passing through. Cell membranes are an example of semi-permeable membranes. Cell membranes allow small molecules such as oxygen, water carbon dioxide and glucose to pass through, but do not allow larger molecules like sucrose, proteins and starch to enter the cell directly.

Example: If there was a semi-permeable membrane with more water molecules on one side as there were on the other, water molecules would flow from the side with a high concentration of water to the side with the lower concentration of water. This would continue until the concentration of water on both sides of the membrane were equal (dynamic equilibrium is established).

Osmosis plays an important role in the human body, especially in the gastro-intestinal system and the kidneys. Osmosis helps you get nutrients out of food. It also gets waste products out of your blood.

Osmosis can occur in both the small and large intestines, with the large intestine being the site of the majority of osmosis. Food travels from the esophagus to the stomach and then to the small intestine as it is processed by your body. Our body absorbs critical nutrients through osmosis.

https://bio.libretexts.org/Learning_Objects/Worksheets/Biology_Tutorials/Diffusion_and_Osmosis

E.g. root hair cells in plants take in nitrate ions from the soil. Their concentration are often higher inside the root hair cell than in the soil, so the diffusion gradient is from the root hair à the soil. Despite this, the root hair cells still can take nitrate ions in, by active transport.

The active transport is done using carrier (transporter) proteins in the cell membrane. These use energy from the breakdown of ATP to move the ions into the cell. The carrier proteins are ATPases. Each carrier protein is specific to just one type of ion or molecule. Cells contain many different carrier proteins in their membranes.

The exocytosis process delivers proteins, lipids, and carbohydrates to the plasma membrane or the extracellular space to sustain plant cell growth, development, and response to environmental stimuli.

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