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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 ...
Bamboo's user avatar
  • 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 ...
Forest's user avatar
  • 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 ...
alex_d's user avatar
  • 241
10 votes
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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 ...
Imtiaz Raqib's user avatar
  • 1,278
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 ...
WYSIWYG's user avatar
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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 ...
WYSIWYG's user avatar
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7 votes
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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 ...
S Pr's user avatar
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7 votes
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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 ...
Ben Bolker's user avatar
  • 5,364
6 votes
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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 ...
another 'Homo sapien''s user avatar
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 ...
Alejandro Vignoni's user avatar
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 ...
Ben Bolker's user avatar
  • 5,364
6 votes
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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 ...
Zlira's user avatar
  • 341
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 ...
pascal's user avatar
  • 604
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 ...
Alejandro Vignoni's user avatar
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. ...
Bryan Krause's user avatar
  • 46k
6 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 ...
shigeta's user avatar
  • 28.3k
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, ...
Roland's user avatar
  • 5,705
5 votes
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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 ...
AliceD's user avatar
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5 votes
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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, ...
JayCkat's user avatar
  • 2,922
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 ...
John's user avatar
  • 14.7k
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,...
KaPy3141's user avatar
  • 1,597
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 $...
Daniel Weissman's user avatar
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, $\...
Ben Bolker's user avatar
  • 5,364
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 ...
Untitpoi's user avatar
  • 354
4 votes

Is it possible to determine the initial population given the final one?

For the logistic equation, $$\frac{\mathrm{d}N(t)}{\mathrm{d}t} = rN(t)\left(\frac{K - N(t)}{K}\right)$$ the solution that allows you to calculate population population size at any time is: $$N(t) = \...
Chris Moore's user avatar
4 votes
Accepted

Which approach is the common one in the literature for determining the bacterial growth rate?

The simple logistic function that you are using here is a fine first-order approximation for modeling microbial growth. Both logarithmic and linear scales are reasonable, with different tradeoffs as ...
jakebeal's user avatar
  • 6,987
4 votes
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There are some species that grow throughout their lives -- is there evidence that even in adulthood their brains increase in size?

Your question falls into an area of study known as allometry. It is generally believed that brain size must increase as body size increases1,2. This relationship has been demonstrated in fish 3,4, ...
tyersome's user avatar
  • 5,598

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