Simple diffusion question

[oreoeater82]

---

Members don't see this ad.

Hey i was wondering about this question...


Which of the following substances probably would not cross a membrane by simple diffusion? A. Hemoglobin
B. Glucose
C. Water
D. Ethanol
E. Chloride ion

​

Answer:
[SIZE=+1]B: [/SIZE] Glucose is such a large molecule that it needs to be transported actively across a membrane.

So my question is... isn't hemoglobin a much larger molecule than glucose? i understand why glucose will not cross a membrane by simple diffusion. After all, we know that glucose transport proteins exist in the membranes of many cells. But shouldn't the answer be A and B?

 

[peyman2002]

I dont like this question, chloride ion needs a transport protein to cross a membrane, just like sodium needs a protein membrane.
glucose definitely needs a protein mem.
Hemoglobin can cross a mem with the help of vesicles, exo and endocytosis which needs ATP

 

[yuppers]

I dont like this question, chloride ion needs a transport protein to cross a membrane, just like sodium needs a protein membrane.
glucose definitely needs a protein mem.
Hemoglobin can cross a mem with the help of vesicles, exo and endocytosis which needs ATP

Some very small ions can cross without a transport protein... I think. One reason Na+ needs a transport for protein is that it is against the concentration gradient for example the neuron's during an action potential.

 

[Danny289]

I dont like this question, chloride ion needs a transport protein to cross a membrane, just like sodium needs a protein membrane.
glucose definitely needs a protein mem.
Hemoglobin can cross a mem with the help of vesicles, exo and endocytosis which needs ATP

^ doesn't count simple diffusion.
agree. I dislike this question. it makes more sense if we take out Hemogolbin. 🙂

 

[peyman2002]

Some very small ions can cross without a transport protein... I think. One reason Na+ needs a transport for protein is that it is against the concentration gradient for example the neuron's during an action potential.

not necessarily, even when its moving down its concentration gradient it still needs a protein membrane.