Todos os organismos necessitam de água e grande parte deles vive em rios, lagos e oceanos. Os processos biológicos, como respiração e fotossíntese, exercem profunda influência na química das águas naturais em todo o planeta. O oxigênio é ator dominante na química e na bioquímica da hidrosfera. Devido a sua baixa solubilidade em água (9,0 mg/l a 20 °C) a disponibilidade de oxigênio nos ecossistemas aquáticos estabelece o limite entre a vida aeróbica e anaeróbica. Nesse contexto, um parâmetro chamado Demanda Bioquímica de Oxigênio (DBO) foi definido para medir a quantidade de matéria orgânica presente em um sistema hídrico. A DBO corresponde à massa de O2| em miligramas necessárias para realizar a oxidação total do carbono orgânico em um litro de água.
BAIRD, C. Química Ambiental. Ed. Bookmam, 2005 (adaptado).
Dados: Massas molares em g/mol: C = 12; H = 1; O = 16.
Suponha que 10 mg de açúcar (fórmula mínima CH2O e massa molar a 30 g/mol) são dissolvidos em um litro de água; em quanto a DBO será aumentada?
Questões relacionadas
- Química | 2.6 Eletroquímica
O cromo é usado na galvanoplastia revestindo estruturas metálicas pelo processo de eletrodeposição. 867 mg de cromo metálico foram depositados sobre um metal em solução ácida que contém óxido de cromo VI sob corrente de 5 A.
CrO3(aq) + 6H+(aq)+6e-- ->Cr(s) + 3 H2O
Assinale a alternativa que contém o tempo necessário para a realização desse processo.
Dados: 1F = 96.500 C; Cr: 52 g/mol; O: 16 g/mol.
- Geografia | 6.2 Energia
Disponível em: https://www.skyscrapercity.com. Acesso em: 12 jul. 2019 (adaptado).
Nas regiões assinaladas, estão instalados os principais parques geradores de energia:
- Língua Inglesa | 1.4 Reading Strategies
Read the text below, from Scientific American (SA), and choose the best option for the questions.
INTERVIEW WITH PAUL NURSE*
This biologist has followed his interests from "fur and feather" to cell cycles and cancer control
Paul Nurse is one of Britain's most distinguished scientists today. 1His groundbreaking work on the cell cycle in the 1970s and '80s revealed how cells make the decisions to grow and divide, thus laying the foundation for a MOLECULAR UNDERSTANDING OF CANCER. 2This has earned him numerous honors, including the LASKER BASIC MEDICAL RESEARCH AWARD in 1998, and many regard him a prime candidate for the NOBEL PRIZE. Since 1996, Sir Paul, who WAS KNIGHTED last year, has also been director-general of the largest cancer research organization in the U.K., the IMPERIAL CANCER RESEARCH FUND (ICRF).
(was knighted = foi condecorado como cavaleiro)
SA: When did you decide to become a scientist? Was that quite early, or only at university?
PN: Well, I think actually already as a schoolchild. I remember seeing Sputnik 2 when I was in London. As a young child, eight or nine years old, I read about it in the newspaper and went out in our garden and saw Sputnik 2 fly over, I think in 1957 or 1958, and this was truly amazing. And then when I was a little older I became interested in natural history, and I watched birds, and I collected beetles, and was interested in plants and so on. So my main entrée into biology was through natural history. I think that is quite common.
SA: Was it always clear you wanted to become a biologist, not a physicist or an astronomer?
PN: Yes, but originally I was more interested in natural history and ecology, and then I found it so difficult, because the laboratory of this field [pointing to the grass] is too uncontrolled. So as I grew older, as an undergraduate and then as a postgraduate, I really wanted to work more on molecular and cellular things, because you could do controlled experiments so much better.
SA: Who do you consider your most important teacher?
PN: I had a very good teacher of biology at school, who I recently met again actually, a man called Keith Neal. Then I think a very important person was my postdoctoral advisor, when I was in the University of Edinburgh, Professor Murdoch Mitchison, who gave me great freedom as a young investigator and allowed me to work in my own way. I owe him great debt for that. He encouraged me, he spoke to me, but he really made no attempt to control me, a very good situation.
SA: You are mostly famous for your work on the CELL CYCLE, the cell machinery that controls cell division in eukaryotes. Could you explain what your most important discovery was?
PN: I think the most interesting discovery that I made was to identify components of what is now sometimes called the cell cycle engine. All humans are made up of billions of cells, and they grow and divide. The process that brings about the reproduction of cells is called the cell cycle. I have been interested for many years in what controls progression through that cell cycle, what regulates the cell division process.
SA: You have two daughters, is either one planning to be a scientist?
PN: I have two daughters, that is true. One of them is, at the moment, a sports journalist at our local television station in Oxford, and the other is in her final year at Manchester University doing theoretical physics. So I have one who is a scientist and one who isn't.
SA: Did you ever encourage them to become scientists?
PN: No, but I would be quite pleased if one of them did. But I think they should make up their own minds.
SA: I also know you are a pilot. Do you think flying an airplane and heading a research institute have anything in common, or is it very different?
PN: It's very different, and I think that's why I am attracted to it. I am a glider pilot, mainly, and I fly gliders when I can at the weekend. It's really to do something totally different, having to concentrate on totally different sorts of things, like keeping this airplane up, and going in the right direction, and finding the up currents. It's a major relaxation because it is so different from what I do normally.
SA: Do you think you will always work on the cell cycle?
PN: I am still working on the cell cycle, but I also have a new area, which is related to the cell cycle, which is cell morphogenesis, or how a cell obtains its form, its shape. I think this is another very fundamental biological problem, like the cell cycle, which I find very interesting. It has some relevance to cancer also, because when cancer cells metastasize and spread through the body, they have to undergo a variety of cell shape changes to be able to escape from their tissue and to get into other places. But the basic mechanisms that control cell shape are simply not understood.
SA: Have you had any personal experience with cancer in your family or among friends, and did that change your view of cancer research?
PN: Because I am director-general of ICRF, it actually means that I meet now many people that have been affected by cancer. So although in my own family I have not, one of my friends certainly has. He survived, but that was really a tough time, and it was quite an experience for me.
It makes me realize that cancer isn't simply an academic problem, that it is a problem that obviously influences in very important ways people's lives, and I think that changes the way you view the research that goes on in an institute.
SA: Do you think we will see a cure for cancer like our grandparents saw a cure for infectious diseases?
PN: I don't, actually. Cancer, first of all, is many different diseases, many different sites and forms; some people say it is as many as 200 different diseases. There are many different genes that can become defective to give rise to cancer, and they all have different characteristics. So I think the likelihood of having a common treatment for all of these is just not likely. There will be some treatments that will be useful across the board, but I think it would be a mistake to look for "the cure" to cancer. But what I think we can expect to see is steady improvement by applying this new knowledge to treating and preventing the disease.
*Paul Nurse was awarded the 2001 Nobel Prize for Medicine.
Scientific American: Interviews: Paul Nurse: June 26, 2000
"False friends" are words in a foreign language which are similar in form to words in our mother tongue, but which do not have the same meaning. Which pair of words below (taken from the text) contains ONLY false friends?
- Matemática | 3.6 Exponencial
Em uma região, uma pessoa que recebe uma notícia falsa (popularmente conhecida pela expressão em inglês fake news) em uma rede social a espalha para outras cinco pessoas que ainda não haviam recebido a notícia.
Para minimizar o impacto, uma campanha de conscientização acerca dos perigos das fake news foi lançada pelo governo com o objetivo de reduzir esse número para quatro.
Se a campanha obtiver sucesso, após n gerações de retransmissão, o número de pessoas a entrarem em contato com uma notícia falsa será reduzido
- História | 3.1 Antiguidade Oriental
196º — Se alguém arranca o olho a um outro, se lhe deverá arrancar o olho.
197º — Se ele quebra o osso a um outro, se lhe deverá quebrar o osso.
198º — Se ele arranca o olho de um liberto, deverá pagar uma mina.
199º — Se ele arranca um olho de um escravo alheio, ou quebra um osso ao escravo alheio, deverá pagar a metade de seu preço.
Código de Hamurabi. Disponível em: www.dhnet.org.br. Acesso em: 6 dez. 2017.
Esse trecho apresenta uma característica de um código legal elaborado no contexto da Antiguidade Oriental explicitada no(a)