1.1 Introduction to Cells Flashcards
Cell theory states that:
All living things are composed of cells (or cell products)
The cell is the smallest unit of life
Cells only arise from pre-existing cells
The cell is the smallest unit of life
Specialized structures within cells (organelles) carry out different functions. Organelles cannot survive alone.
Cells only arise from pre-existing cells:
Cells multiply through division
All life evolved from simpler ancestors
Mitosis results in genetically identical diploid daughter cells
Meiosis generates haploid gametes (sex cells)
Cells vary considerably in size and shape but they share common features:
Cell membrane
Genetic material
Have enzyme-catalysed chemical reactions
Creates energy through chemical reactions that power the cell
striated muscle
Muscle cells called fibres can be very long (30mm)
They are surrounded by a single plasma membrane but they are multi-nucleated (many nuclei).
aseptate fungal hyphae
challenges the idea that a cell is a single unit.
Fungal hyphae are very large with many nuclei and a continuous cytoplasm
The tubular system of hyphae form dense networks called mycelium
The cytoplasm is continuous along the hyphae with no end cell wall or membrane
giant algae (Acetabularia)
Gigantic in size (5-100mm) - one would expect them to be composed of many cells
Complex in form, it consists of three anatomical parts:
Bottom rhizoid (that resembles a set of short roots)
Long stalk
Top umbrella of branches that may fuse into a cap
The single nucleus is located in the rhizoid
Characteristics of Living Things
Metabolism - the web of all the enzyme-catalysed reactions in a cell or organism, e.g. respiration
Response - Living things can respond to and interact with the environment
Homeostasis - The maintenance and regulation of internal cell conditions, e.g. water and pH
Growth - Living things can grow or change size / shape
Excretion – the removal of metabolic waste
Reproduction - Living things produce offspring, either sexually or asexually
Nutrition – feeding by either the synthesis of organic molecules (e.g. photosynthesis) or the absorption of organic matter
How does paramecium show the functions of life?
Excretion – the plasma membrane control the entry and exit of substances including expulsion of metabolic waste
Metabolism – most metabolic pathways happen in the cytoplasm
Nutrition – food vacuoles contain organisms the parameium has consumed
Homeostasis – contractile vacuole fill up with water and expel I through the plasma membrane to manage the water content
Growth – after consuming and assimilating biomass from food the paramecium will get larger until it divides.
Response – the wave action of the cilia moves the paramecium in response to changes in the environment, e.g. towards food.
Reproduction – The nucleus can divide to support cell division by mitosis, reproduction is often asexual
How does chlorella show the functions of life?
Excretion – the plasma membrane control the entry and exit of substances including the difussion out of waste oxygen
Metabolism – most metabolic pathways happen in the cytoplasm
Nutrition – photosynthesis happens inside the chloroplasts to provide the algae with food
Reproduction – The nucleus can divide to support cell division, by mitosis (these cells are undergoing cytokinesis)
Growth – after consuming and assimilating biomass from food the algae will get larger until it divides.
Response – the wave action of the cilia moves the algae in response to changes in the environment, e.g. towards light.
Homeostasis – contractile vacuole fill up with water and expel I through the plasma membrane to manage the water content
Small SA:V ratio
Substances cannot enter cell quickly
Waste accumulates
Cells may overheat if metabolism produces heat faster than it is lost
Large SA:V ratio
Cell can be more efficient
More SA to supply each unit of volume
Shorter diffusion pathway
Are there cases when large SA:V ratios are disadvantageous?
Small, warm-blooded mammals lose heat very quickly with a high SA:V ratio. They need to eat almost constantly!
Desert plants would lose too much water with flat leaves that have a high SA:V ratio. This is why they decrease the SA of leaves by making fatter leaves.
So how do organisms maximise the SA:V ratio?
Cells divide rather than grow bigger (also allows cells to specialise)
Folded membranes are used to increase SA (recall the folds in mitochondria)
Folded tissues to increase SA (recall the villi in the small intestine)
Emergence
a property observed in livings that occurs when an entity is observed to have properties its parts do not have on their own.
“The whole is greater than the sum of the parts”. Multicellular organisms are capable of completing functions that individual cells could not undertake - this is due to the interaction between component parts (cells) producing new functions.
