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CELL MEMBRANE

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Biology

Cells

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133 Terms

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CELL MEMBRANE

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  • A vital component of all living cells, which separates the cell's contents

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from the outside environment.

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  • Semi-permeable phospholipid bilayer, allowing the entry and exit of

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certain molecules while blocking other molecules; selectively permeable.

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  • Other functions of the cell membrane:

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o Physical barrier

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o Communication and signaling

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o Nutrient uptake and waste removal

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o Cell shape and stability

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o Cell-cell interactions

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ATENEO DE DAVAO UNIVERSITY

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Km 7 Central Park Blvd, Talomo, 8016 Davao City, Philippines

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Tel No. +63 (82) 221.2411 local 8608

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E-Mail: shs@addu.edu.ph * www.addu.edu.ph

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In Consortium with Ateneo de Zamboanga University and Xavier University

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SENIOR HIGH SCHOOL – BIOLOGY AND EARTH & LIFE SCIENCE CLUSTER

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  1. PASSIVE TRANSPORT

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o A type of cellular transport that moves substances across the cell

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membrane without the need for energy expenditure.

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o Occurs along the concentration gradient, which is the difference in

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concentration of a substance between two areas, particularly from

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an area of high concentration to an area of low concentration.

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o No net movement will occur after the solute molecules have

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reached dynamic equilibrium where the molecules continue to

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cross the membrane in both directions but at equal rates.

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o There are three types:

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i. Simple Diffusion - net movement of a substance from an

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area of higher concentration to an area of lower

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concentration

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▪ Does not require the input of energy. The concentration

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gradient alone is sufficient to drive the movement of

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molecules

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▪ Molecules move freely and randomly, colliding with each

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other and spreading out to achieve a uniform distribution

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▪ Involved in various biological processes, such as the

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delivery of oxygen, water, and other small molecules to

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cells in the body

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▪ Factors that affect simple diffusion:

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● Temperature – higher temperatures, faster diffusion

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● Concentration gradient – greater difference in

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gradient, faster diffusion

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● Molecular size and weight – smaller molecules

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diffuse faster

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● Solubility – more soluble molecules in a solvent

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diffuse quicker

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● Membrane permeability – membranes that are more

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permeable to a particular molecule will allow for faster

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diffusion

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ATENEO DE DAVAO UNIVERSITY

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Km 7 Central Park Blvd, Talomo, 8016 Davao City, Philippines

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Tel No. +63 (82) 221.2411 local 8608

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E-Mail: shs@addu.edu.ph * www.addu.edu.ph

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In Consortium with Ateneo de Zamboanga University and Xavier University

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SENIOR HIGH SCHOOL – BIOLOGY AND EARTH & LIFE SCIENCE CLUSTER

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ii. Facilitated Diffusion - allows molecules to move across a

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cell membrane with the help of specific transmembrane

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integral proteins

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▪ Does not require energy

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▪ Transport proteins assist in the diffusion of molecules,

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either by carrier proteins or channel proteins.

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● Carrier proteins – bind to specific molecules and

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undergo a conformational or shape change, which

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allows the molecule to pass across the proteins. Ex.

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Glucose transporter

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● Channel proteins – form pores or channels which

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allow specific molecules to pass across the

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membrane. Ex. Aquaporins

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▪ Factors that affect facilitated diffusion:

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● Concentration gradient – greater difference in

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gradient, faster rate of diffusion

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● Temperature – higher temperatures, faster diffusion

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rates

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ATENEO DE DAVAO UNIVERSITY

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Km 7 Central Park Blvd, Talomo, 8016 Davao City, Philippines

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Tel No. +63 (82) 221.2411 local 8608

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E-Mail: shs@addu.edu.ph * www.addu.edu.ph

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In Consortium with Ateneo de Zamboanga University and Xavier University

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SENIOR HIGH SCHOOL – BIOLOGY AND EARTH & LIFE SCIENCE CLUSTER

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● Saturation – once all transport proteins are in use,

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maximum rate of diffusion is achieved and cannot

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increase further

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● Selectivity – each channel or carrier protein can only

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transport specific molecules

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iii. Osmosis - diffusion of solvent, usually water molecules,

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across a selectively permeable membrane, driven by the

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concentration gradient

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▪ Osmotic pressure – pressure of a solution needed to keep

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it in equilibrium with pure water

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▪ Passive process; does not require energy

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▪ Occurs across a selectively permeable membrane, which

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allows the passage of water molecules but restricts the

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passage of solutes

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▪ Regulates water balance in cells and uptake of water in

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plant roots

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▪ Factors that affect osmosis:

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● Concentration gradient – the greater the difference

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of concentrations, the faster the rate of osmosis

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● Temperature – an increase in temperature increases

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the rate of osmosis

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