Cell Growth

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# Cell Growth - PowerPoint PPT Presentation

The blue whale is the largest mammal in the world. The pygmy shrew is 1 of the smallest mammals in the world. How does the size of an average cell compare between the two?.

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## PowerPoint Slideshow about ' Cell Growth' - nida

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Presentation Transcript

The blue whale is the largest mammal in the world. The pygmy shrew is 1 of the smallest mammals in the world.

How does the size of an average cell compare between the two?

A. the average cell of a blue whale is smallerthen the average cell of a pygmy shrew. B. the average cell of a blue whale is largerthen the average cell of a pygmy shrew.C. the average cell of a blue whale is about the same size as the average cell of a pygmy shrew.

Cell Growth
• When an organism grows, the number of cells increase, but the size of each cell remains small!

### Cell Growth & Division

Surface Area to Volume Ratio

When organism’s grow, the number of cells increases (increasing the surface area of cells in the body), but the volume of each cell will stay the same!

Cell Models
• Compare the cells & make your calculations.

SA = L x W x 6 sides

Volume = L x W x H

Which cube has the largest surface area?

Which cube has the largest volume?

Which cube has the largest SA/V ratio?

Surface Area to Volume

1

6

6

24

8

3

54

27

2

1

216

216

As you increase the size of the cube, what increases more quickly – surface area or volume?

Surface Area to Volume Ratio
• As cells increase their size, their volume (the cytoplasm & organelles) increases faster than their surface area (cell membrane)!
• Since the volume of the cell (& its need for nutrients) increases faster than the surface area (supplies the nutrients), the demand will eventually outgrow the supply!
• So, cells need a large SA/V ratio!
Limits to Cell Growth
• DNA “Overload”: the larger a cell becomes, the more demands the cell places on its DNA
• When a cell is small, DNA can easily control the cell’s functions & meet its needs.
• If a cell is too large, it still only has 1 copy of DNA, so it is more difficult for the cell to perform its functions!

A tall person will have more skin cells than me, but the size of our skin cells is the same!

Limits to Cell Growth
• Exchanging Materials: if a cell is too large, it’s difficult to get enough oxygen & nutrients in & waste products out
• Large cells have more trouble moving substances across the cell membrane!
What happens if a cell gets too large?

Cell Division!

• When a cell gets too large, it:
• Makes a copy of its DNA (replication), & then…
• Divides to form 2 “daughter” cells
Cell Division
• Cell division in eukaryotes is more complex than in prokaryotes!
• There are 2 stages of eukaryotic cell division:
• Mitosis: division of the cell nucleus
• Cytokinesis: division of the cell cytoplasm
The Cell Cycle
• The series of events that a cell goes through as it grows & divides is called the cell cycle!
• When a cell is NOT dividing, it is said to be in interphase.
Events of the Cell Cycle
• Interphase, when the cell is NOT dividing, has 3 phases:
• G1
• S
• G2
Interphase – G1 Phase
• Period of activity in which cells do most of their growing
• Cells increase in size.
• Cells synthesize (make) new proteins & organelles.
Interphase – S Phase
• DNA is replicated.
Interphase – G2 Phase
• Organelles & molecules required for cell division are produced.
M Phase – AFTER Interphase
• M Phase is the phase of cell division! This includes:
• Mitosis (division of the nucleus)
• Cytokinesis (division of the cytoplasm)

### Chromosomes

Chromosomes
• Every somatic (body) cell contains identical genetic information!
• DNA is replicated & passed on from parent cell to daughter cells!

All of your somatic cells (all body cells except egg & sperm) contain the same 46 chromosomes!

Chromosomes
• Chromatin: DNA & the proteins it is wrapped around
• Chromosomes: condensed chromatin
Chromosomes
• The cells of every organism have a specific number of chromosomes!

Humans have 46 chromosomes per cell (23 from mom & 23 from dad)!

Chromosomes
• Chromosomes are only visible during cell division, when they are condensed!
• The rest of the time, the chromatin is spread throughout the nucleus.
Chromosomes
• Before cell division, each chromosome is replicated.
• When a chromosome is replicated, it consists of 2 identical sister chromatids.
• When a cell divides, the chromatids separate, & 1 goes to each of the 2 new cells.
• Sister chromatids are attached to each other at the spot called the centromere.
Chromosomes
• At the ends of each chromatid is an area called the telomere.
• Filled with non-coding DNA
• Like a protective cap
• Gets shorter during each cell division
• Shortening is believed to be linked to aging!
What are some reasons that cells undergo cell division?
• Growth
• Repair
• Maintenance
• Asexual Reproduction
Asexual Reproduction
• 1 cell reproducing by itself
• Making a “clone” – an identical copy
• Binary Fission: organism replicates its DNA & divides in half, producing 2 identical daughter cells
• Bacteria
• Budding: asexual process by which yeasts increase in number
Asexual Reproduction
• Unicellular organisms reproduce asexually by mitosis or something similar to mitosis.
• Prokaryotes (bacteria) can’t do mitosis!
• The daughter cells are identical to the parent cells.