VCE Biology Question Thread

[maheenkhan]

Hello!
I have a question about anaerobic respiration.
I know that glycolysis is an anaerobic process since no oxygen is required. Then, fermentation occurs, which is lactic acid fermentation in muscle cells or alcoholic fermentation in yeast cells.
What is the reason for anaerobic respiration not proceeding to the Krebs Cycle? I thought no oxygen is used in the Krebs Cycle but it is required for the electron transport chain.
Thanks!

[PhoenixxFire]

Hello!
I have a question about anaerobic respiration.
I know that glycolysis is an anaerobic process since no oxygen is required. Then, fermentation occurs, which is lactic acid fermentation in muscle cells or alcoholic fermentation in yeast cells.
What is the reason for anaerobic respiration not proceeding to the Krebs Cycle? I thought no oxygen is used in the Krebs Cycle but it is required for the electron transport chain.
Thanks!

Hey,

For Krebs to occur you need NAD+ to generate NADH. That NADH is then turned back into NAD+ in the electron transport chain (which can't occur without oxygen). If Krebs kept going you'd run out of NAD+, and Krebs can't occur without it.

[f0od]

Hey! I had two questions I'm not 100% certain about

1. What type of transport is used when water from a salt lake moves into a halophytic (salt loving) bacterial cell and why?

2. From and to which parts of the stimulus response model do negative feedback occur?

Any help would be greatly appreciated, thanks!

[darkz]

Hey! I had two questions I'm not 100% certain about

1. What type of transport is used when water from a salt lake moves into a halophytic (salt loving) bacterial cell and why?

2. From and to which parts of the stimulus response model do negative feedback occur?

Any help would be greatly appreciated, thanks!

1. When talking about water, the method of transport should always be referred to as being osmosis
2. The negative feedback system is no longer examinable for VCE, however it's essentially the process in which the stimulus (the variable) is being constantly monitored and assessed. Therefore, if a change is detected, i.e. a deviation from the norm value, then the homeostatic mechanism is brought into place to reverse the change. We can use blood glucose levels as an example. If the blood glucose level deviates and becomes lower than it should, then that would be detected and glucagon would then be secreted by the alpha cells of the pancreas.

Stimulus = low blood sugar levels
Receptor = alpha cells of the pancreas? Don't remember exactly - but basically just a detector for low blood glucose levels
Effector = alpha cells secrete glucagon
Response = glucagon causes blood glucose levels rise

[Rameen]

Hi,

Do ALL bacteria have double membranes like mitochondria and chloroplast or just an internal membrane?

[PhoenixxFire]

Hi,

Do ALL bacteria have double membranes like mitochondria and chloroplast or just an internal membrane?

Nope not all bacteria have a double membrane. The double membrane found in mitochondria and chloroplasts is thought to come from the vesicle that formed around them when they were engulfed by a cell, this is part of the evidence that supports the symbiotic theory.

[darkz]

Hi,

Do ALL bacteria have double membranes like mitochondria and chloroplast or just an internal membrane?

Mitochondria and chloroplast only have a double membrane because it is hypothesised that they were ingested by another organism. Hence, their outer membrane is that of the host, and the inner membrane is their original one.

However, in relation to your question, no, not all bacteria have double membranes. Here's a good explanation if you need further elaboration:
https://biology.stackexchange.com/questions/74494/do-all-bacterial-cells-have-a-double-membrane

[Rameen]

Nope not all bacteria have a double membrane. The double membrane found in mitochondria and chloroplasts is thought to come from the vesicle that formed around them when they were engulfed by a cell, this is part of the evidence that supports the symbiotic theory.

Mitochondria and chloroplast only have a double membrane because it is hypothesised that they were ingested by another organism. Hence, their outer membrane is that of the host, and the inner membrane is their original one.

However, in relation to your question, no, not all bacteria have double membranes. Here's a good explanation if you need further elaboration:
https://biology.stackexchange.com/questions/74494/do-all-bacterial-cells-have-a-double-membrane

Oh okay thank you!
So is one piece of evidence for the endosymbiotic origin of chloroplasts and mitochondria that they have an internal membrane similar to bacteria?

[darkz]

Oh okay thank you!
So is one piece of evidence for the endosymbiotic origin of chloroplasts and mitochondria that they have an internal membrane similar to bacteria?

Correct! Also because by having two membranes, it suggests that they entered the cell via endocytosis.

[f0od]

1. When talking about water, the method of transport should always be referred to as being osmosis
2. The negative feedback system is no longer examinable for VCE, however it's essentially the process in which the stimulus (the variable) is being constantly monitored and assessed. Therefore, if a change is detected, i.e. a deviation from the norm value, then the homeostatic mechanism is brought into place to reverse the change. We can use blood glucose levels as an example. If the blood glucose level deviates and becomes lower than it should, then that would be detected and glucagon would then be secreted by the alpha cells of the pancreas.

Stimulus = low blood sugar levels
Receptor = alpha cells of the pancreas? Don't remember exactly - but basically just a detector for low blood glucose levels
Effector = alpha cells secrete glucagon
Response = glucagon causes blood glucose levels rise

Thank you for the reply!

1. Yeah, I thought it was related to osmosis but I wasn't sure if the mention of the salt changed anything at all – Would the water be entering the cell as it is salt-loving and the water is salty?

2. Wow, thanks so much for the information! I had no idea that it was out of the course (I should probably read the study guide haha) Thanks heaps for the example as well!

[darkz]

Thank you for the reply!

1. Yeah, I thought it was related to osmosis but I wasn't sure if the mention of the salt changed anything at all – Would the water be entering the cell as it is salt-loving and the water is salty?

2. Wow, thanks so much for the information! I had no idea that it was out of the course (I should probably read the study guide haha) Thanks heaps for the example as well!

To answer the question, you need to establish the difference in concentration of salt, as that is what effectively causes osmosis to occur - because the bacteria is salt-loving, we are able to assume that the concentration of salt within it will be higher than its surroundings. Therefore, as osmosis goes from low solute concentration -> high solute concentration, water will move into the bacteria.

[PhoenixxFire]

Thank you for the reply!

1. Yeah, I thought it was related to osmosis but I wasn't sure if the mention of the salt changed anything at all – Would the water be entering the cell as it is salt-loving and the water is salty?

Halophytic organisms actually have some weird adaptions to prevent them losing all their water due to the high salt concentration surrounding them. Most halophytic bacteria have osmoprotectants in their cytoplasm. Osmoprotectants change the osmolarity of the cytoplasm to prevent all of the water leaving the cell. So the water movement still occurs via osmosis, the concentration gradient of salt just isn't what you'd expect it to be (there can be a higher concentration of salt outside the bacteria, but water can still move in via osmosis).

For VCE, unless you're given information saying otherwise in the stem of the question, just assume that all water movement is via osmosis.

[vox nihili]

Halophytic organisms actually have some weird adaptions to prevent them losing all their water due to the high salt concentration surrounding them. Most halophytic bacteria have osmoprotectants in their cytoplasm. Osmoprotectants change the osmolarity of the cytoplasm to prevent all of the water leaving the cell. So the water movement still occurs via osmosis, the concentration gradient of salt just isn't what you'd expect it to be (there can be a higher concentration of salt outside the bacteria, but water can still move in via osmosis).

For VCE, unless you're given information saying otherwise in the stem of the question, just assume that all water movement is via osmosis.

This was a rude return to first year Biology jeeeeees

[Erutepa]

Hi guys! Here with a bit of an open ended research question.
Note: this is unit 1 work, so don't consider it all too urgent (aside from me being a moron and the work probably being due today).
For our practical assignment we had to orchestrate an experiment, and for the theory, we have to put it into a scientific poster. I have majority of the poster made - introduction to results - and am currently working on some sources. However! I have come to the discussion part and I've hit a standstill.

My hypothesis was proven wrong and this is something I definitely should have asked my teacher about before the holidays started, but I didn't have the chance, and now, I don't know why. Long story short and without being overly specific; I thought that "more carbon dioxide in a plant's environment = higher rate of photosynthesis/more oxygen produced". The experiment proved me wrong and actually showed that a lower amount is better.

I'm not necessarily looking for people to tell me why, but I would LOVE to know where I should be looking to find the answer/if there are any keywords for it, or if this is even typical/what should have happened. Thank you so much. (Please let me know if this question isn't allowed!)

An increase in carbon dioxide concentration should increase the rate of photosynthesis, unless the rate of the reaction is limited by another factor (I.e. Light intensity or temperature). As such the reaction rate should either stay at the same, or increase.
If it decrease it suggests that you may have
 -  manipulated your IV wrong and may have decreased the co2 concentration
 - failed to control other variables such as temperature or light intensity. If wither of these variables decreased during the experiment, it could explain your results
 - made erroneous measurements of the rate of photosynthesis.

In you discussion you should discuss the mechanisms of photosynthesis and explain why co2 concentration increase should increase the rate of photosynthesis. Theb you should dicusss the potential errors that may have produced your results. When talking about how uncontrolled temperature or light intensity could affect the results, also link back to photosynthesis and explain why this is the case precisely.

Hope this helps!

[Rameen]

Hi
I am having trouble answering the question:
"Explain how the internal structure of chloroplasts helps absorb the maximum amount of light"
Is it because the thylakoid are stacked in grana, so that increases the surface area to absorb light?