C

I think membrane =lipids in middle ,proteins outside.

E

We observed that Microscope showed dark-light-dark.

R

This result suggests that this means proteins outside lipids inside.

E:We observed that the red Fluorescent agent in mouse membrane and the green one in human cells’ will mixed together after few minutes.

R:Therefore, we infer that the membrane is not fixed and that can move around.

C

I think that proteins can move.

E

We saw that brightness in other areas also fade.This also shows that proteins can move around the membrane.

R

Therefore,we infer that proteins can move.

C: I think that the membrane is like a sea of lipids proteins floating in it.

E: According to the freeze-fracture,they saw proteins inside the lipid bilayer.

R: Therefore,we infer that the membrane is not fixed.

E:According to the experiment by James David Robertson in 1959 using an electric microscope, the membrane was observed to have three layers:dark-light-dark. This matched t purposed sandwich model.

E：According to the FRAP experiment, scientists bleached a small part of the cell membrane and saw that the area slowly became bright again. This means new proteins moved into the area. And another FLIP experiment, scientist kept bleaching one part of membrane, that brightness in other areas also faded.

R：Therefore, we infer that proteins in the membrane can move around.

I think the membrane are made up of two layers of lipid.

E.

According to the two scientists ,Evert Groter and Feancois , their experiment shows us how much lipid they measured and the cell membrane consists of two layers of lipids.

R.

Because the sale membrane can let fat-soluble substance enter cells easily. We infered sales membrane made up of two layers of lipids.

The fluid mosaic model describes the cell membrane as a lipid bilayer with proteins that can move freely.

Evidence

1. 1966 – Branton’s freeze-fracture showed proteins in the lipid bilayer.

2. 1970 – Frey and Edidin found membrane proteins can move.

3. 1972 – Singer and Nicolson proposed the fluid mosaic model.

Reasoning

These findings show the membrane is dynamic, with mobile proteins embedded in lipids, explaining its flexible structure and function.

The “sandwich model” (1935–1959) proposed that proteins coat both sides of the lipid bilayer.

Evidence

In 1935, Hugh Davson and James Danielli suggested this structure to explain membrane function. In 1959, James David Robertson’s electron microscopy revealed a dark–light–dark pattern matching the model.

Reasoning

This evidence supported the idea that proteins are integral to membrane structure, making the sandwich model widely accepted at the time.

---

The cell membrane is composed of a lipid bilayer made of two layers of lipid molecules.

Evidence

19th-century plasmolysis showed a membrane barrier around the cell.

In 1899, Overton found lipid-soluble substances entered cells more easily, suggesting the membrane is mainly lipids.

In 1925, Gorter and Grendel measured lipid content in red blood cells and found it was twice that needed for a single layer, proving a bilayer.

Reasoning

Plasmolysis demonstrated the membrane’s barrier role, Overton identified lipids as its main component, and Gorter & Grendel provided direct evidence of a bilayer. Together, these findings established the lipid bilayer model.

According to the experiment that tested which substances could pass through the cell,the result showed that fat-soluble substances entered the cell more easily. Another experiment using red blood cells measured the amount of lipid and found that the cell membrane consists of not one but two layers of lipid.Therefore we infer that the cell membrane is structured as a lipid bilayer.

25莊耕誼

27郭鎮宇

29陳宇崴

30黃子毅

35蔡秉樺

Proteins in the cell membrane can move laterally.

Evidence:

• FRAP: After bleaching a small membrane area, brightness recovered as unbleached proteins moved in.

• FLIP: Continuous bleaching of one area caused other areas to lose brightness.

Reasoning:

Both experiments show that proteins diffuse within the membrane, supporting the fluid mosaic model.

According to an experiment with mouse and human cells,scientists labeled the proteins and found that they could move around.

This result suggests that the membrane is not fixed.

The sandwich Model proposes that the cell membrane is formed by proteins covering both sides of a lipid bilayer .

• Evidence

     In 1935, Hugh Davson and James Danielli suggested that proteins were important and covered the lipid bilayer like a sandwich to explain membrane function.

     In 1959, James David Robertson used an electron microscope and observed the membrane had a "dark-light-dark" three-layered structure .

• Reasoning

Robertson's "dark-light-dark" observation matched the Sandwich Model, leading to its increased popularity.