19
votes
Why do seeds grow upwards?
Because of a force known as geotropism - it is a reaction to gravity. The upward growth of shoots from seeds is known as negative geotropism whereas the downward growth of roots is known as positive ...
- 376
14
votes
Accepted
Are the bacteria in the stomachs of unborn babies beneficial?
It's a fascinating topic! While most of the bacteria known to colonize babies comes from the vaginal tract during birth and then later, through breastfeeding, although there is evidence to suggest ...
- 1,879
14
votes
Why do seeds grow upwards?
In addition to the geotropism mentioned in the other answers, experiments on the ISS have shown that plants will grow oriented in a manner such that “upward” (i.e. the stem, leaves, etc.) is toward a ...
- 241
12
votes
Why are cancer rates low in large animals?
Short answer
Large animals do get cancer. They may contract cancer with an incidence less than that estimated by absolute cell numbers, but there seems to be a lack of data on cancer rates in large ...
- 52.3k
10
votes
Accepted
Biggest change in size from birth
@JM97 is correct.
According to National Geographic >>
The gestation period of a Red Kangaroo is 33 days and it's baby at birth weighs a mere 0.03 oz. To put it into a more precise perspective, on ...
- 1,268
7
votes
Are thunder and lightning necessary for any organisms?
Lightning results in nitrogen fixation (Draphco et al., 1967; Hill et al., 1980). It is one of the main abiotic nitrogen fixation mechanisms. As you would know very well, nitrogen fixation is ...
- 35.3k
7
votes
Exponential growth equation and bacteria
Considering your assumption:
I'm just looking at the exponential part, where the simple exponential
equation works. If we assume there's sufficient nutrients for bacteria
to grow unchecked for ...
- 35.3k
7
votes
Accepted
What are the evolutionary reasons behind men being taller than women?
I assume by asking why, you are asking about the distal evolutionary causes, and not the molecular mechanisms that account for these things.
(Important disclaimer: these causes are difficult to be ...
- 6,192
7
votes
Accepted
Refuge impact on growth rate
The answer to this depends a lot on what kind of question you're asking. Adding more context/clarifying your question might help you get more useful answers.
If you run a short-term experiment ...
- 5,324
6
votes
Accepted
Effect of transpiration on plant growth
Simple Answer: There is no simple answer, because transpiration is just one of many factors that affect plant growth, and even in controlled experiments, the conclusions deviate according to different ...
- 14.1k
6
votes
How do I determine this logistic growth model formula?
The growth of the yeast can be studied with a Logistic model (i.e. differential equation) as follows:
$$
\frac{dX}{dt}=\mu X \left(1 - \frac{X}{X_{max}} \right)
$$
This is an ordinary differential ...
6
votes
What are the evolutionary reasons behind men being taller than women?
More details to support @SPr's answer, from the abstract of Plavcan (2012): "Sexual Size Dimorphism, Canine Dimorphism, and Male-Male Competition in Primates: Where Do Humans Fit In?"
While ...
- 5,324
6
votes
Accepted
What happens to plants if they are exposed to "sunlight" 24h a day?
This review (from 2011)1 states that it depends on the plant species and cultivar.
Some continuous light (CL)-grown photosynthetic organisms show
increased productivity. However, CL also induces ...
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6
votes
Why is DNA replication so much faster in prokaryotes than eukaryotes?
The difference in DNA replication rate between prokaryotes and eukaryotes is still under current research, but the basics are understood. It is very much a matter of complexity, as eukaryotes are more ...
- 594
6
votes
Is there a favoured mathematical model of bacterial growth?
Some clarifications:
Commonly used models for bacterial isothermal growth curves (which represent the growth curve directly) are for example:
Exponential
Logistic
Generalized logistic
The Monod ...
6
votes
Larval abalone devlopmental times - what does ~ °C.days or °C hr-1 mean
From e.g.
Fukazawa, H., Kawamura, T., Takami, H., & Watanabe, Y. (2007). Oogenesis and relevant changes in egg quality of abalone Haliotis discus hannai during a single spawning season. ...
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5
votes
Database of cancer cells
The National Cancer Institute (NCI) has a list of doubling times for a variety of commonly used cell lines, see
https://dtp.cancer.gov/discovery_development/nci-60/cell_list.htm
I my experience, ...
- 5,675
5
votes
Accepted
Do brain cells regenerate in the adult brain?
Short answer
Neural regeneration in the adult brain is confined to two localized hot spots, namely the hippocampus and the anterior lateral ventricular wall. Establishing connectivity between new ...
- 52.3k
5
votes
Accepted
Why are humans only so tall/large?
The question is a bit vague but I will take it to mean the following
Why does it (the body) stop in terms of height or physical mass when it can still keep on growing?
The answer is physics, ...
- 2,916
5
votes
What is the mechanism through which fractals arise in plants and animals?
because fractals are emergent structures created by simple rules, as are many biological structures. The same kind of simple recursive signals that lead to fractals are simple enough to be stumbled on ...
- 14.3k
5
votes
Is there a favoured mathematical model of bacterial growth?
the more biologically grounded Monod growth
Why is the Monod model more biologically grounded? It is empiric and NOT based on biological considerations! I only know this equation from enzyme kinetics,...
- 1,597
5
votes
Accepted
Is it viable to make liquid potassium ferilizer through dissolving very small amounts of potassium chloride in water
the issue here is the chloride not the potassium. Potassium chloride is very soluble in water. but you could be killing your crops/garden when you spray it on.
Most plants do not tolerate much ...
- 28.1k
4
votes
Accepted
Modeling population growth - Variance
Check out Kendall (1949), section 2. He shows that the pdf is a geometric distribution. In your notation, it's $P_n(t) = N(0)W^{-t}\left(1-W^{-t}\right)^{n-1}$, which implies that the mean is indeed $...
- 641
4
votes
Modeling population growth - Variance
If $W$ is a parameter, I'd expect (in the simplest case) that $W$ itself is a constant (i.e. it doesn't have a distribution). (By the way, I would normally use $T_{1/2}$ to denote the doubling time, $\...
- 5,324
4
votes
Accepted
Does the bending of a tree's trunk in the wind stimulate and strengthen root growth?
In tree growth there is principle called The axiom of universal stress whereby the growth is in such a way as to equalise the stress across the whole of its structure. The roots, the stem and the ...
- 936
4
votes
Accepted
Which algae grow fastest under optimal conditions?
The answer to your question depends on many variables. To narrow down the list of possible species it might be helpful to list under which conditions you intend to grow this algae and whether you want ...
- 1,415
4
votes
Can you accelerate the growth of a plant by accelerating its surroundings?
This is not the best answer, but see that as a starter! Feel free to use my answer to build yours!
I have found a so-called professor speaking of advantages to go on a 24h light/12h dark cycle (36h ...
- 354
Only top scored, non community-wiki answers of a minimum length are eligible