Cell Size · 细胞大小
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| volume/ˈvɒljuːm/ | 体积 | tǐ jī |
| surface area/ˈsɜːfɪs ˈeərɪə/ | 表面积 | biǎo miàn jī |
| surface-area-to-volume ratio/ˈsɜːfɪs ˈeərɪə tə ˈvɒljuːm ˈreɪʃɪəʊ/ | 表面积与体积比 | biǎo miàn jī yǔ tǐ jī bǐ |
| diffusion/dɪˈfjuːʒn/ | 扩散 | kuò sàn |
Why cells stay tiny
- Almost every cell is microscopic, whether in a mouse or an elephant.
- A big animal is not made of big cells — it is made of more cells.
- There is a hard physical reason cells cannot grow large.
- It comes down to a race between surface and volume.
细胞为什么保持微小
- 几乎每个细胞都是显微镜下才能看到的,无论在老鼠还是大象身上。
- 大动物不是由大细胞构成的——它由更多细胞构成。
- 细胞无法长大,有一个硬性的物理原因。
- 这归结为表面和体积之间的一场赛跑。
Surface versus volume
- A cell takes in food and oxygen across its surface area 表面积.
- It uses those materials throughout its whole volume 体积.
- As a cell grows, its volume grows faster than its surface.
- So a big cell has too little surface to feed its large inside.
表面对体积
- 细胞通过它的表面积(surface area)吸收食物和氧气。
- 它在整个体积(volume)里使用这些物质。
- 当细胞长大时,它的体积增长得比表面更快。
- 所以大细胞的表面太少,喂不饱它庞大的内部。
A cube of side 2 has surface area 24 and volume 8. What is its SA:V ratio (surface ÷ volume)? · 一个边长为 2 的立方体,表面积是 24,体积是 8。它的表面积体积比(表面积 ÷ 体积)是多少?
$24 \div 8 = 3$. A smaller cube (side 1) would give $6 \div 1 = 6$ — a higher ratio. · $24 \div 8 = 3$。更小的立方体(边长 1)会给出 $6 \div 1 = 6$——更高的比值。
The SA:V ratio falls
- The surface-area-to-volume ratio 表面积与体积比 measures surface per unit of inside.
- Double the size of a cube and this ratio is cut in half.
- A small cell has a high ratio — plenty of surface for its volume.
- A large cell has a low ratio — not enough surface to keep up.
表面积体积比下降
- 表面积体积比(surface-area-to-volume ratio)衡量每单位内部有多少表面。
- 把一个立方体的大小翻倍,这个比值就减半。
- 小细胞比值高——相对于它的体积有充足的表面。
- 大细胞比值低——表面不够跟得上。
Surface area : volume · 表面积 : 体积
Grow the cube and watch the SA:V ratio fall — the reason cells and exchange surfaces stay small. · 把立方体变大,看表面积体积比下降——这就是细胞和交换表面保持小的原因。
Why must most cells stay very small? · 为什么大多数细胞必须保持很小?
A small cell has a large surface area relative to its volume · 体积, so materials diffuse in and out fast enough. · 小细胞相对于它的体积有大的表面积,所以物质进出扩散得足够快。
As a cell gets bigger, its surface-area-to-volume ratio falls. · 当细胞变大时,它的表面积体积比下降。
Volume grows faster than surface area, so the SA:V ratio falls as size increases. · 体积比表面积增长得更快,所以随着大小增加,表面积体积比下降。
Diffusion sets the limit
- Materials cross the cell by diffusion 扩散, which is only fast over short distances.
- In a large cell, the centre is too far from the surface.
- Supplies would arrive too slowly to keep the cell alive.
- So staying small keeps every part close to the surface.
扩散决定上限
- 物质通过扩散(diffusion)穿过细胞,而扩散只在短距离上快。
- 在大细胞里,中心离表面太远。
- 供应会到得太慢,无法维持细胞的生命。
- 所以保持小,让每个部分都靠近表面。
What sets the size limit for a cell relying on diffusion? · 对一个依靠扩散的细胞,是什么决定了它的大小上限?
Diffusion is only fast over short distances, so a cell too large cannot supply its centre quickly enough. · 扩散只在短距离上快,所以太大的细胞无法足够快地供应它的中心。
Select all · 所有 true statements about cell size. · 选出关于细胞大小的所有正确说法。
Bigger cells exchange materials more slowly per unit volume, not faster. The other three are correct. · 更大的细胞按单位体积计算交换物质更慢,不是更快。其余三条正确。
Bigger is not better for exchange. A larger cell has less surface for each unit of its volume, so it exchanges materials more slowly, not faster. This is exactly why cells divide instead of growing without limit.
对交换来说,更大不是更好。更大的细胞每单位体积的表面更少,所以它交换物质更慢,而不是更快。这正是细胞分裂而不是无限制生长的原因。
Why exchange surfaces are folded:
- Your lungs must swap huge amounts of oxygen quickly.
- A smooth balloon would have far too little surface.
- Instead the lung is folded into millions of tiny sacs — a giant surface packed into a small volume.
交换表面为什么是折叠的:
- 你的肺必须快速交换大量的氧气。
- 一个光滑的气球表面会远远太少。
- 于是肺被折叠成数百万个微小的气囊——把巨大的表面塞进很小的体积。
Cells stay small because a small cell has a high surface-area-to-volume ratio. As size grows, volume rises faster than surface area, so the ratio falls and diffusion can no longer supply the centre fast enough. Big organisms use more cells, not bigger ones.
细胞保持小,是因为小细胞有高的表面积体积比。随着大小增长,体积比表面积上升得更快,所以比值下降,扩散不再能足够快地供应中心。大生物用更多细胞,而不是更大的细胞。